Glossary

This glossary defines the terms that come up most often in parts buying, repair, and sourcing across the categories GetPartFound covers (trucks, tractors, small engines, appliances, and fabrication). Each entry is short, practical, and written for someone who is actively trying to fix something, not for a textbook.

The glossary will grow over time. If there’s a term you’d like to see added, let me know via the Contact page.

Contents

Aftermarket

A replacement part made by a company other than the original equipment manufacturer, and sold outside the vehicle or equipment manufacturer’s official dealer channel. Aftermarket parts range widely in quality. Some are made to or beyond OEM specifications. Others are cheaper substitutes that may not last as long. The aftermarket exists because dealer-sold parts are usually more expensive and because some failure modes are best solved by specialty vendors who improve on the original design.

See also: OEM, Genuine, OE Replacement.

Casting number

An alphanumeric code physically cast or stamped into a metal part during manufacturing. Casting numbers are distinct from catalog or service part numbers. You’ll find them on engine blocks, cylinder heads, intake manifolds, transmissions, axle housings, and many other major castings. They identify the part’s foundry origin, production date range, and design revision. Casting numbers are especially valuable in classic and vintage restoration, where the original catalog number may have been superseded or lost decades ago but the casting number on the part itself still tells you exactly what it is. A 1965 Ford engine block, for example, can be authenticated as period-correct or identified as a later replacement entirely from its casting number.

See also: Cross-reference, Supersession.

Core / Core charge

A deposit charged when you buy a remanufactured part such as an alternator, starter, or fuel injector. The deposit is refunded when you return the old, broken part for the manufacturer to rebuild. The “core” is the salvageable old unit. If you don’t return it, you forfeit the deposit. Core charges are common on parts where the housing or major components can be reused, and remanufacturers depend on a steady supply of cores to operate.

See also: Reman, Rebuilt.

Cross-reference (number) / Interchange

An alternate part number that identifies the same physical part across different manufacturers, catalogs, or eras. For example, a Ford part with number FL3Z-9943300-A might cross-reference to a Motorcraft, NAPA, or Dorman part number that fits the same vehicle. Knowing the cross-reference lets you compare prices across catalogs and find the part in suppliers that don’t use Ford’s numbering. Cross-references are especially valuable when an OEM part is discontinued or backordered. Mechanics and some forums use the term “interchange” or “interchanges” to mean the same thing; the two terms are used interchangeably.

See also: NLA, Supersession.

Donor part / Donor vehicle / Parts-out

A part removed from a vehicle, equipment piece, or appliance that has been deliberately stripped for its components. The vehicle or equipment being stripped is the “donor,” and the resulting individual components are “donor parts.” The verb form is “parts-out” — a totaled truck might be parted out by a salvage yard, generating dozens of donor parts that get sold individually. Donor parts are common in restoration projects where new replacement parts no longer exist, and in cases where a single sub-component (a particular sensor, a rare body trim piece) is needed and a full assembly purchase is impractical. They are genuine OEM parts with unknown remaining lifespan, similar to pulls but typically sourced through more specialized channels (restoration networks, dedicated parts-out auctions, marque-specific forums).

See also: Pull, NLA, NOS.

Fitment

The specific range of vehicles, equipment, or applications a part is designed to fit. Fitment usually specifies year range, make, model, trim or sub-model, and any optional equipment that affects fit (such as 4WD vs 2WD, or trucks with or without a particular package). Always verify fitment before ordering. A part that “fits a 2019 F-250” might only fit certain configurations of that truck.

See also: VIN-specific.

Friction-fit / Press-fit

A connection that holds together through mechanical friction or pressure alone, with no fasteners, adhesive, or threads. Many small plastic parts (caps, plugs, trim pieces) are friction-fit, meaning they push onto a post or into a hole and stay through interference between the two surfaces. Friction fits loosen over time as plastic shrinks or wears, which is why caps and plugs eventually fall off or break.

Genuine

A part sold by the vehicle or equipment manufacturer in their branded packaging through their authorized dealer network. A “Genuine Ford” part comes in a Ford-branded box from a Ford dealer, regardless of who actually manufactured it. Genuine parts carry the manufacturer’s warranty and are generally the most expensive option because dealer markup is included in the price. The physical part inside a Genuine box is often identical to the OEM supplier’s own-brand version sold elsewhere for less money.

See also: OEM, Aftermarket.

NLA (No Longer Available)

Short for “No Longer Available.” A part status used by manufacturers and dealers when a part has been discontinued and is no longer in production or distribution channels. NLA does not mean the part is impossible to find; it means the manufacturer’s official supply has run out. Used pulls, NOS in dealer back-stock, donor parts from parted-out vehicles, and aftermarket reproductions are common paths to sourcing an NLA part. NLA status is the inflection point where most repair stories get hard, and where this site’s approach (cross-references, donor sourcing, fabrication) starts to matter most. Owners of vehicles or equipment more than 10 to 15 years old will see NLA on dealer parts lookups regularly.

See also: NOS, Pull, Donor part, Cross-reference.

New Old Stock (NOS)

Brand new parts that have been sitting unused in a warehouse, dealer, or distributor for years, often after the part was discontinued. NOS parts are valuable for older vehicles where current production parts no longer exist. They are physically identical to original parts because they came from the same production runs. Pricing varies widely: common NOS parts can be cheap; rare ones, especially for classic or collector vehicles, can be expensive.

See also: NLA, Pull, Genuine.

OE / OE Replacement / OE Quality

Marketing terms used by aftermarket manufacturers to claim their parts match the original equipment in form, fit, and function. “OE Replacement” and “OE Quality” do not mean the part is OEM. They mean the manufacturer made it to OEM specifications (or claims to). Quality varies. Read product reviews and check whether the seller is a known supplier or a generic listing before trusting these labels.

See also: OEM, Aftermarket.

OEM (Original Equipment Manufacturer)

The company that manufactures a part, often as a contractor for a vehicle or equipment manufacturer. Bosch, Magna, Denso, and Aisin are examples of OEMs that supply parts to multiple vehicle manufacturers. When someone says “OEM part,” they technically mean a part made by the OEM, which may or may not be sold under the vehicle manufacturer’s brand.

A part made by Magna and sold in a Ford-branded box is both OEM and Genuine. The same part made by Magna and sold under Magna’s own brand outside the dealer channel is OEM but not Genuine. A part made by a generic copy manufacturer is neither OEM nor Genuine. It is aftermarket.

Understanding this distinction is one of the most valuable things in parts buying. The “OEM, not Genuine” channel often sells the same physical part at half the dealer price.

See also: Genuine, Aftermarket.

Pull / Take-out

A used part removed from a vehicle, equipment piece, or appliance, usually one that was scrapped or parted out. Pulls are typically sold through eBay, salvage yards, or specialty used-parts dealers. They are genuine OEM parts but have unknown remaining lifespan. A pull from a low-mileage vehicle may be nearly new; one from a high-mileage vehicle may have very little life left. Pull pricing is typically 30 to 60 percent of new Genuine pricing.

See also: Donor part, NLA, Genuine, NOS.

Rebuilt

Similar to remanufactured but less standardized. A rebuilt part has had its failed or worn components replaced, but the work may have been done by a small shop or even an individual, and the quality control is less consistent than a reman from a large industrial operation. Rebuilt parts can be excellent or terrible depending on who did the work. Always research the rebuilder before buying. The terms “reman” and “rebuilt” are sometimes used interchangeably, but “reman” generally implies a more industrial, standardized process.

See also: Reman, Core charge.

Reman / Remanufactured

A used part that has been completely disassembled, cleaned, inspected, and rebuilt with all wearing components replaced to factory specifications. Reman parts are common for high-cost mechanical assemblies like alternators, starters, transmissions, and fuel injectors. A quality reman part should be functionally equivalent to new and typically costs 40 to 60 percent less. Reman parts almost always involve a core charge: you pay a deposit at purchase and get it back when you return the old broken unit.

See also: Rebuilt, Core charge.

Sub-assembly vs assembly

An assembly is a complete unit (an engine, a tailgate handle assembly, a washing machine motor). A sub-assembly is a component group within that larger unit (a piston in the engine, a cap on the handle, a bearing in the motor). Manufacturers vary widely in whether they sell sub-assemblies separately or only as part of the full assembly.

Ford, for example, often catalogs at the assembly level, meaning a five-dollar broken sub-component might force you to buy a two-hundred-dollar full assembly. Understanding which level a manufacturer catalogs at is one of the most useful things to know when sourcing parts, because it determines whether the aftermarket is your only practical option.

Supersession

When a manufacturer replaces one part number with a different one over time. The new number “supersedes” the old. Supersessions happen when a part is redesigned, when manufacturing changes, or when multiple older part numbers are consolidated into one new number. Always order by the most recent superseded number. Parts catalogs and dealer systems will route old numbers to the current one automatically, but informal listings on eBay or in forum threads may still reference the obsolete number.

See also: Cross-reference, NLA, Casting number.

Torque spec

The specific tightening force, measured in foot-pounds or Newton-meters, that a fastener must be tightened to during installation. Torque specs are critical for parts that experience cyclic stress (head bolts, wheel lugs, suspension components). Under-torque means the fastener can loosen and fail; over-torque means the fastener can stretch, strip, or break. Always look up the manufacturer’s torque spec for the specific application. Generic “tight enough” tightening is one of the most common sources of failure in DIY repair.

VIN-specific

A part that fits only certain vehicles within a model year range based on the VIN (Vehicle Identification Number). Modern manufacturers often produce running changes mid-year, so two trucks built in the same year can take different parts. VIN-specific parts require providing the seller with your full VIN to verify fit. This is most common for electronic components like control modules and sensors that need programming, and for emissions parts that vary by destination market.

See also: Fitment.

This glossary is updated as new terms come up across the site. If there’s something you’d like to see added or clarified, send a note via the Contact page.