- Mash (collapse)
- Structural damage that is a change in LENGTH — the structure is shortened or folded, usually from a front or rear impact.
- Sag (kickup)
- Structural damage that is a change in HEIGHT — part of the structure drops below or rises above its datum dimension, often at the cowl or rails.
- Sidesway (sway)
- Structural damage that is a change in WIDTH — the structure shifts off the centerline to one side, leaving uneven side-to-side measurements.
- Twist
- Damage in which one corner of the structure is higher and the diagonally opposite corner lower — the structure is no longer flat. Found with diagonal/datum measurements.
- Diamond
- Damage in which one side rail is driven rearward relative to the other, making the structure a parallelogram. Found with X (cross) diagonal measurements.
- Kink
- A sharp, abrupt crease or fold (radius about equal to or smaller than the metal's thickness). A kink is repaired by replacing or sectioning, NOT straightening.
- Bend
- A smooth, gradual deformation over a broad area (radius larger than the metal's thickness). A bend can usually be straightened and reused.
- Repair-or-replace rule
- A bend can be straightened; a kink must be replaced or sectioned. The OEM procedure always overrides the general rule.
- Anchoring
- Securing the vehicle to the bench or rack at multiple points so a pull moves only the damaged area, not the whole vehicle.
- Why anchor at multiple points?
- So the correcting force acts on the damage and not the whole car; a single anchor lets the vehicle move instead of the metal.
- Pull in reverse order of impact
- Apply corrective force opposite the way the damage went in, relieving the last damage first, to unfold the structure the way it folded.
- Over-pull (spring-back)
- Pulling slightly past the target so that when the force is released and the metal springs back, it lands on the correct dimension.
- Stress relieving
- Working or warming the metal within allowed limits during a pull to release locked-in stress so it returns toward its original shape and stays there.
- Tram gauge
- A measuring bar with adjustable pointers used to check point-to-point dimensions on a frame or structure against the OEM spec.
- Self-centering gauge
- A hanging gauge with a centerline pin that shows whether structural points line up with the vehicle's centerline by sighting the gauges.
- Full frame (body-on-frame)
- A separate ladder or perimeter frame, common on trucks and some SUVs, to which the body is bolted. Measured and repaired differently from a unibody.
- Perimeter frame
- A full frame whose side rails run around the outer perimeter of the passenger area, with crossmembers tying the rails together.
- Ladder frame
- A full frame with two straight side rails joined by crossmembers like the rungs of a ladder; common on pickups.
- Crossmember
- A structural member that ties the two side rails of a frame together, adding strength and maintaining width.
- Diagonal (X) measurement
- Comparing crossing diagonals of a structure; equal diagonals mean the structure is square, unequal diagonals reveal diamond or sidesway.
- Manufacturer dimension chart
- The OEM's published length, width, and height spec for every structural control point, used as the target for measurement.
- Underbody vs. upperbody damage
- Underbody = floor pan, rails, and crossmembers; upperbody = pillars, roof rails, and aprons. B4 covers diagnosing and repairing both.
- Frame straightening machine
- A bench or rack with anchoring and pulling towers that apply controlled force to restore structural dimensions while the vehicle is measured.
- Pulling tower / pulling post
- The movable post on a frame machine that anchors a chain to apply directional corrective force during a pull.
- Cross-checking measurements
- Comparing matching points on the left and right sides; equal symmetrical readings confirm the structure is straight.
- Documenting a structural repair
- Recording before/after measurements, the procedures followed, and that OEM specs and corrosion protection were restored, to verify the repair.
- Verifying a structural repair
- Re-measuring all control points after the pull to confirm length, width, and height are back within tolerance before refinishing.
- Spring-back
- The tendency of pulled metal to relax back toward its damaged position when force is released; the reason for over-pulling.
- Inertia (chain) damage
- Secondary damage caused as collision energy travels through the structure beyond the point of impact.
- Why measure before, during, and after
- Before to plan the pull, during to monitor progress and avoid over-pulling, after to verify the structure is back to spec.
- Symmetrical vs. asymmetrical vehicle
- Symmetrical = left and right sides mirror each other; asymmetrical = sides differ, so you must use the OEM chart rather than side-to-side comparison.
- Collision energy path
- The route impact force travels through the structure; understanding it tells you where to look for hidden secondary damage.
- Visual inspection of structure
- Looking for buckles, cracks, tears, wrinkled metal, and disturbed corrosion protection as first clues to structural damage.
- Cracked/torn metal at a pull
- A sign the metal has been stretched past its limit; that area generally must be replaced or sectioned rather than pulled further.
- Heat and frame straightening
- Heat may be used within limits on mild steel to relieve stress, but must be strictly limited or avoided on high-strength steel.
- Buckle
- A localized collapse or fold in a structural member caused by compressive collision force.
- Body alignment vs. structural alignment
- Body alignment is panel gaps and fit; structural alignment is the underbody/upperbody dimensions that determine those gaps.
- Restoring corrosion protection (frame)
- Reapplying weld-through primer, anti-corrosion coatings, and seam sealer wherever the original coating was disturbed during repair.
- Order of pulls in complex damage
- Relieve major structural pulls and crush before fine-tuning; correct length, width, and height roughly, then re-measure and refine.
- Why follow OEM repair procedures
- The maker engineered the structure for crash energy management; only the OEM-proven method restores that designed performance.
- Damage analysis
- The systematic inspection and measurement that identifies all primary and secondary damage and determines the repair plan.
- Mash vs. sag vs. sidesway hook
- Mash = length, Sag = height, Sidesway = width. Naming the condition tells you which dimension to restore.
- Hidden damage
- Structural damage not visible from the outside, found only by measuring; collision force can distort points far from the impact.
- Anchoring points (factory)
- Designated pinch-weld or sub-frame locations the OEM specifies for clamping the vehicle to the bench.
- Sectioning vs. straightening a frame
- Straighten a bend back to spec; section or replace a kinked or torn area at an OEM-approved location.
- Unibody (unitized body)
- Construction in which the body panels and structure form a single welded unit that carries the loads, instead of a separate body on a full frame.
- Three-dimensional measurement
- Checking every structural control point in length, width, and height against the maker's dimension chart.
- Datum plane
- An imaginary, perfectly level horizontal plane (usually below the vehicle) from which all HEIGHT dimensions are measured.
- Centerline
- An imaginary line dividing the vehicle into equal left and right halves; the reference for all WIDTH measurements, checked first.
- Body zero / reference point
- A fixed reference (often at the front) from which LENGTH dimensions are measured along the vehicle.
- Why check the centerline first
- It establishes a known symmetrical reference; if the center is off, all width comparisons are meaningless.
- Control point
- A specific structural location (hole, hardpoint, or fixture position) with a published length/width/height dimension on the OEM chart.
- Mechanical measuring system
- Tram and self-centering gauges that compare structural points to the dimension chart by physical measurement and sighting.
- Electronic / computerized measuring
- A system using sensors or a probe and software to compare the damaged vehicle to a stored factory database in real time.
- Laser measuring system
- Uses laser targets and a reference to compare structural points to spec, giving precise three-dimensional readings during the pull.
- Dedicated fixture (bench) system
- Vehicle-specific fixtures that bolt to OEM control points; if a fixture won't fit, that point is out of spec.
- Universal measuring system
- Adjustable measuring equipment set to OEM data, used across many vehicles instead of vehicle-specific fixtures.
- High-strength steel (HSS)
- Steel stronger and thinner than mild steel. It tolerates little heat — heating beyond the OEM limit ruins its strength — so it is often repaired cold or replaced.
- Ultra-high-strength steel (UHSS)
- Very strong steel (boron, martensitic grades) used in the safety cage (B-pillars, rockers). Usually replaced at factory seams, not heated or straightened.
- Boron steel
- An ultra-high-strength steel used in critical safety structures; typically cold-cut and replaced, never heated or pulled.
- HSLA steel
- High-Strength Low-Alloy steel — a common high-strength grade that is stronger than mild steel but more heat-sensitive.
- Heat and high-strength steel
- Heat above the maker's temperature limit destroys the engineered strength of high-strength steel, so heat is limited or avoided.
- Cold straightening
- Pulling high-strength steel without applying heat, within OEM limits, to avoid weakening it.
- Sectioning
- Replacing only part of a structural component by cutting and joining at a location other than a factory seam — only where and how the OEM permits.
- Sectioning location
- Chosen only where the maker allows, using the specified cut and joint; never at random, because the joint must restore original strength.
- Offset butt joint with backing
- A common sectioning joint: the two ends butt together over an inserted backing/sleeve that reinforces the weld.
- Full part replacement
- Removing and replacing a structural part at its factory seams when sectioning is not permitted or practical.
- Factory seam
- An original joint where the maker welded panels together; the default place to separate and replace a structural part.
- Crush zone (crumple zone)
- Structure designed to fold and absorb collision energy; it must be restored to OEM spec so it crushes correctly next time.
- Safety cage (passenger compartment)
- The ultra-high-strength structure (pillars, rockers, roof rails) protecting occupants; usually replaced, not straightened.
- Rail (frame rail)
- A main fore-aft structural member that carries load and manages crash energy; measured in three dimensions during repair.
- Apron / strut tower
- Upperbody structure supporting the suspension and engine cradle; measured to keep wheel alignment and panel fit correct.
- Sub-frame / engine cradle
- A bolt-on or welded structure carrying the engine and suspension; its mounting points are key measured control points.
- Cowl
- The structure at the base of the windshield joining the firewall, fenders, and inner panels; a common sag/datum reference area.
- Pinch weld (structural)
- A flanged, spot-welded structural seam (e.g., rocker) used for anchoring and as a control point.
- Pre-pull measurement
- Recording all control points before pulling so the technician can see every misaligned dimension and plan the corrective force.
- Post-pull verification
- Re-measuring all points after the pull to confirm length, width, and height are within tolerance.
- Tolerance (measurement)
- The acceptable amount a structural dimension may vary from the OEM spec (often a few millimeters) and still be considered correct.
- Aluminum structure
- A structure built of aluminum, which requires an isolated work area, dedicated tools, and often rivet-bonding instead of welding.
- Galvanic corrosion (steel + aluminum)
- Corrosion that occurs when steel and aluminum particles contact; the reason aluminum work is kept in a separate isolated area.
- Rivet-bonding
- Joining structure with structural adhesive plus rivets; common on aluminum and on some steel joints per OEM.
- Self-piercing rivet (SPR)
- A rivet that pierces and joins panels (often aluminum) without a pre-drilled hole, set with a dedicated tool per OEM.
- Why aluminum needs a separate area
- To prevent steel dust from contaminating aluminum and causing galvanic corrosion, and to keep dedicated tools uncontaminated.
- Adhesive bonding (structural)
- Using engineered structural adhesive, often with welds or rivets, where the OEM specifies it to join panels.
- Unibody collision energy travel
- Because the body is one unit, impact force travels through it, so damage and the order of repair often involve the whole structure.
- Setup error in measuring
- Mounting fixtures or gauges incorrectly gives false readings; verifying setup against undamaged points prevents chasing phantom damage.
- Why over-pull a unibody
- Thin high-strength panels spring back when force is released, so a slight over-pull lands the dimension on spec.
- Hardpoint
- A reinforced location (hole or bracket) used as a measuring control point or fixture mount.
- Three-dimensional chart vs. side-to-side
- On asymmetrical vehicles you must use the OEM three-dimensional chart, since the two sides are not mirror images.
- Restoring corrosion protection (unibody)
- Reapplying weld-through primer between mating flanges, anti-corrosion coatings, and seam sealer after structural repair.
- Why thin HSS reduces heat allowance
- Thin, hardened steel loses strength quickly with heat, so straightening relies on measurement and cold pulling, not heat.
- Identify the steel first
- Before cutting, heating, or pulling, identify the metal (OEM data) so you use a procedure that won't destroy its strength.
- Measuring system database
- The stored OEM dimensions in an electronic/computerized system used to compare the damaged vehicle in real time.
- Length, width, height per point
- Each control point on the chart has all three dimensions; a point can be correct in two and out in the third.
- When not to section
- Where the OEM prohibits sectioning or the part is ultra-high-strength; then replace at factory seams.
- Welded vs. bolted structural parts
- Some structural parts are bolt-on (cradle, bumper reinforcement) and others welded; replacement method follows the original.
- Strut/shock tower measurement
- Critical for wheel alignment; small structural shifts here change alignment angles, so they are measured carefully.
- Pre-repair scan / measurement plan
- Inspecting and measuring to build a complete repair plan before any cutting or pulling begins.
- Why measurement beats muscle
- Three-dimensional measurement, not pulling force, is what makes a structural repair correct and verifiable.
- Stationary (fixed) glass
- Glass bonded permanently to the body — the windshield and back glass — as opposed to movable door glass.
- Urethane adhesive
- The structural adhesive that bonds stationary glass to the body; it contributes to structural integrity and air-bag performance.
- Structural role of the windshield
- A bonded windshield adds to roof-crush resistance and helps proper passenger air-bag deployment, so the bond is structural.
- Pinchweld (glass)
- The flanged body edge around a glass opening to which the glass is bonded; must be cleaned, trimmed, and primed.
- Full cut vs. partial cut (old urethane)
- Trim the old urethane to a thin, even layer rather than to bare metal, giving the new bead a compatible surface to bond to.
- Why leave a thin urethane layer
- Fresh urethane bonds best to the original cured urethane, so a thin layer is left rather than cutting to bare metal.
- Priming bare metal (glass)
- Any bare metal exposed on the pinchweld must be primed to prevent corrosion and ensure the urethane adheres.
- Glass frit / primer
- The black ceramic band on the glass edge; it and the glass are primed so the urethane bonds and is protected from UV.
- Safe drive-away time (SDAT)
- The time the urethane needs to cure to a strength that will hold the glass in a crash before the vehicle can be returned.
- Why observe drive-away time
- Releasing the vehicle early risks the glass not holding in a crash, compromising occupant protection and air-bag function.
- Urethane bead
- The continuous, correctly shaped (often V-shaped) bead of urethane applied to bond the glass with the right gap and strength.
- Setting the glass
- Aligning and seating the glass on the bead with even pressure and correct positioning before the urethane skins over.
- Cold knife / wire-out removal
- Tools used to cut the old urethane and free a bonded glass for removal without damaging the pinchweld.
- Modular glass
- Glass that comes as an assembly (with moldings/encapsulation) and is bonded as a unit to the body opening.
- Contamination and bonding
- Oil, dust, or moisture on the pinchweld or frit weakens the urethane bond, so surfaces are cleaned per the adhesive maker.
- Gasket-set vs. bonded glass
- Older glass used a rubber gasket; modern stationary glass is urethane-bonded and structural, requiring proper prep.
- Why use the specified urethane
- Only the specified high-modulus structural urethane meets the strength and drive-away requirements for the structural bond.
- Air-bag and the windshield bond
- The passenger air bag can deploy against the windshield, so a poor bond can let the glass push out and reduce protection.
- Inspecting glass for leaks
- After install, checking for water leaks and wind noise confirms a continuous, properly seated urethane bead.
- Glass moldings / reveal
- The trim around stationary glass; reinstalled correctly so the bond and appearance are maintained.
- Encapsulated glass
- Glass with a molded-in trim/molding edge; handled and bonded so the encapsulation and seal stay intact.
- Pinchweld damage before glass
- Bent or corroded pinchweld is repaired and primed before bonding, since the bond is only as good as the surface.
- Glass removal safety
- Wearing cut protection and supporting the glass so it does not fall while cutting it free from the urethane.
- Temperature/humidity and cure
- Urethane cure speed and safe drive-away time depend on temperature and humidity per the adhesive maker's chart.
- One-part vs. two-part urethane
- One-part cures with moisture in air; two-part cures chemically and can reach drive-away strength faster.
- Why not bond over dirty old urethane
- Loose or contaminated old urethane breaks the chain of adhesion, so it is trimmed to a sound, clean thin layer.
- GMAW (MIG) welding
- Gas Metal Arc Welding — feeds a continuous wire electrode with shielding gas; the most common structural steel welding method.
- Shielding gas (GMAW)
- Gas (often a CO2/argon mix for steel) that shields the molten weld from air to prevent porosity and weak welds.
- STRSW
- Squeeze-Type Resistance Spot Welding — clamps steel between copper electrodes and passes current to make a spot weld, duplicating factory welds with low heat.
- Why STRSW is preferred
- It recreates the original factory joining method and adds little heat, preserving the strength of high-strength steels.
- MIG brazing
- A lower-temperature joining method using a silicon-bronze filler, specified by some makers for high-strength steel to avoid heat damage.
- Why MIG brazing for HSS
- Its lower heat input reduces the heat-affected zone and protects the engineered strength of high-strength steel.
- Plug weld
- A weld made through a hole drilled or punched in the top panel to join it to the panel beneath, simulating a spot weld.
- Butt weld
- A weld joining two pieces edge-to-edge in the same plane; used in sectioning, often with backing for strength.
- Lap weld
- A weld joining two overlapping panels along the overlap edge.
- Test weld (coupon)
- A practice weld on the same metal and thickness as the repair to verify the welder is set up to make a full-strength weld.
- Why make test welds
- Destructive testing of a coupon confirms penetration and strength before welding the actual structure.
- Weld penetration
- How deeply the weld fuses into the base metal; too little is weak, too much can burn through thin high-strength steel.
- Weld porosity
- Gas pockets in a weld (from contamination or poor shielding) that weaken it; a reason to clean metal and check shielding gas.
- Heat-affected zone (HAZ)
- The area around a weld whose properties change from welding heat; minimized on high-strength steel by limiting heat.
- Weld-through primer
- A conductive zinc primer applied between mating flanges so the joint can be welded while still protected from corrosion.
- Cutting tools (structural)
- Reciprocating saws, plasma cutters, and spot-weld cutters used to remove damaged structure with controlled heat and minimal collateral damage.
- Spot-weld cutter
- A tool that drills out factory spot welds to separate panels at a seam without distorting the surrounding metal.
- Plasma cutting and HSS
- Plasma cuts quickly but adds heat, so it is used carefully (often only for removal) on heat-sensitive high-strength steel.
- Cleaning metal before welding
- Removing paint, rust, coatings, and oil so the weld fuses cleanly and is free of porosity.
- Weld distortion
- Warping from welding heat; controlled with stitch/skip welding, clamping, and limiting heat input.
- Stitch (skip) welding
- Welding in spaced intervals and letting the metal cool to reduce heat buildup and distortion on thin panels.
- Aluminum welding (GMAW / spool gun)
- Aluminum is welded with a spool gun or push-pull feeder and argon shielding, in an isolated area with dedicated tools.
- Polarity (GMAW steel)
- GMAW typically uses DC electrode positive (reverse polarity) for good penetration on steel.
- Backing strip / insert
- Metal placed behind a butt joint (especially in sectioning) to reinforce the weld and control penetration.
- Corrosion protection after welding
- Restoring weld-through primer, anti-corrosion coatings, and seam sealer on all welded structural joints.
- PPE for welding
- Welding helmet with the correct shade, gloves, and fire-resistant clothing, plus protecting glass, trim, and airbags from heat.
- Protecting electronics during welding
- Disconnecting the battery and protecting modules so welding current does not damage vehicle electronics.
- Resistance welding electrodes
- The copper tips on a resistance spot welder that conduct current and squeeze the panels; kept clean and dressed for good welds.
- Why joining method must match metal
- The wrong weld or too much heat on high-strength steel destroys the strength the structure relies on for crash performance.
- Wire feed speed and voltage
- GMAW settings that control heat and deposition; set per metal thickness and confirmed with a test weld.
- Burn-through
- Melting a hole through thin metal from too much heat; avoided with correct settings and skip welding.
- Squeeze pressure (STRSW)
- The clamping force of the electrodes; correct pressure and current make a sound resistance spot weld nugget.
- Weld nugget
- The fused button of metal formed at a spot weld; its size indicates the joint's strength.
- Grinding welds
- Dressing structural welds carefully without removing so much that the joint is weakened.
- Why protect airbags/glass when welding
- Welding heat and sparks can damage airbags, glass, and trim, so they are removed or shielded.
- Joint fit-up
- Properly aligning and gapping panels before welding so the weld has the right penetration and strength.
- OEM weld locations
- Makers specify number, size, and location of welds for a structural part; the repair duplicates them.
- Cutting at the correct location
- Cutting only where the OEM allows (factory seam or approved sectioning point) to keep the joint strong.
- Cosmetic vs. structural welds
- Structural welds must restore strength to spec; cosmetic welds (non-load-bearing) have less demanding requirements but still must hold.
- Why disconnect the battery
- Prevents welding current from finding a path through and damaging vehicle electronics and modules.
- Plastic identification
- Identifying a plastic by its molded ISO code, a burn or float test, or maker info before choosing a repair method.
- ISO code (plastic)
- The standardized identification code molded into a part (e.g., TPO, PP, ABS, PUR) that tells the plastic type and repair method.
- Thermoplastic
- A plastic that softens and can be reshaped or welded each time it is heated, so it can be repaired by plastic welding or adhesive.
- Thermoset plastic
- A plastic cured into a permanent shape that cannot be remelted, so it is repaired only with structural adhesives, not heat welding.
- Thermoplastic vs. thermoset hook
- Thermoplastics can be welded (they remelt); thermosets cannot be remelted, so they are adhesive-repaired.
- TPO (thermoplastic olefin)
- A common flexible thermoplastic used for bumper covers; weldable and repairable with the matching rod or adhesive.
- PP (polypropylene)
- A common thermoplastic for bumpers and trim; identified by ISO code and repaired by welding or adhesive.
- ABS plastic
- A rigid thermoplastic used for interior and some exterior parts; weldable with matching rod or repaired with adhesive.
- PUR / RIM plastic
- Polyurethane (often reaction-injection-molded) used in flexible parts; commonly repaired with two-part adhesives.
- Plastic (airless/hot-air) welding
- Joining thermoplastics by melting the base and a matching filler rod with hot air or an airless welder.
- Match the weld rod to the plastic
- The filler rod must be the same plastic family as the part, or the weld won't fuse and will fail.
- Two-part adhesive repair
- Mixing a resin and hardener to bond and rebuild plastic; common for thermosets and flexible covers.
- Flexible vs. rigid adhesive
- Flexible adhesive is used on parts that flex (bumper covers) so the repair moves with the part instead of cracking.
- V-groove (plastic repair)
- Grinding a V into a crack from both sides creates surface for the weld or adhesive to bond and rebuild strength.
- Reinforcing with mesh/cloth
- Embedding fiberglass cloth or metal mesh in the adhesive on the backside to strengthen a plastic repair.
- Burn test (plastic)
- Observing flame color, smoke, and odor of a small sample to help identify the plastic when no ISO code is present.
- Float (water) test
- Some plastics (like polyolefins) float in water, helping distinguish them from denser plastics during identification.
- Adhesion promoter (plastic)
- A primer applied to certain plastics (like olefins) so adhesive or paint will bond to the otherwise low-energy surface.
- Cleaning plastic before repair
- Washing with soap and water, then a plastic cleaner, to remove mold-release agents and contamination before bonding.
- Surface prep for plastic
- Cleaning, sanding/grinding, and applying adhesion promoter as needed so the repair material bonds to the plastic.
- Why identify plastic first
- It decides whether the part can be welded (thermoplastic) or must be adhesive-repaired (thermoset) and which materials to use.
- Bumper cover (fascia)
- Usually a flexible thermoplastic; repaired with flexible adhesive or welding and refinished with flex additives.
- SMC (sheet molded compound)
- A rigid thermoset composite used on some panels; repaired with structural adhesives, not heat welding.
- Backside repair
- Reinforcing the hidden back of a cracked plastic part with adhesive and mesh before finishing the visible front.
- Flex additive (refinishing plastic)
- An additive mixed into primer/paint so the finish flexes with the part and does not crack.
- Plastic repair vs. replacement
- Many bumper covers and trim parts can be repaired more cheaply than replaced when the damage is repairable.
- Heat damage to plastic
- Too much heat distorts or burns plastic; welding temperature is matched to the plastic so it melts without scorching.
- Sanding/grinding a plastic crack
- Removing material around the crack to bare, clean plastic and creating a bevel so the repair material grips.
- Why not weld a thermoset
- Thermosets cannot remelt, so heat welding fails; they must be joined with structural adhesive.
- Identifying with maker information
- Service information or the part catalog can confirm the plastic type when the ISO code is unclear.
- Documenting structural repairs (overall)
- Recording measurements, materials, procedures, and corrosion protection so the repair can be verified to OEM spec.
- Why OEM procedures override rules of thumb
- The maker engineered the structure; published procedures reflect testing the general rule may not, so they take priority.
- Restoring NVH and seals
- Replacing seam sealer, sound deadeners, and foam fillers disturbed in repair so noise, vibration, and water control return to factory.
- Final structural quality check
- Re-measuring, inspecting welds and corrosion protection, and confirming OEM procedures before releasing the vehicle.
- Verify-and-document mindset
- A correct B4 repair is measured, OEM-procedure-driven, corrosion-protected, verified by re-measurement, and documented.
