In Body-in-White automotive manufacturing, repeatable part location is the foundation of dimensional quality. NAAMS locating pins are the standardized hardware that makes that repeatability possible—across suppliers, fixtures, and production lines. This guide covers what the NAAMS standard is, the full range of pin types and series codes, round vs. diamond pin geometry, retractable pins, material and coating specifications, and how to select the right pin for your fixture application.
What is the NAAMS standard?
NAAMS stands for North American Automotive Metric Standard. It was created through a collaborative effort among automotive OEMs, steel manufacturers, and tooling suppliers to standardize the metric components used in Body-in-White (BiW) assembly and stamping tooling across the North American automotive industry.
The standard defines exact dimensional specifications, tolerances, materials, coatings, and NAAMS code numbering for a wide range of fixture components—including locating pins, retainers, clamps, supports, and more. The objective is to optimize Body-in-White designs, processes, and tooling while reducing costs and complexity across the supply chain.
- ▸Full metric dimensioning—all NAAMS pins are fully metric, eliminating inch/metric conversion errors across global supply chains
- ▸Standardized code system—each pin is identified by a NAAMS code (e.g., APQ103) that encodes series, diameter, and options, laser-etched directly on the pin for traceability
- ▸Interchangeability—any NAAMS-compliant pin from any NAAMS supplier is a drop-in replacement; no custom drawing required
- ▸Perpendicularity tolerance—NAAMS standard requires the pin to be perpendicular to the datum surface within 0.015mm T.I.R.
- ▸Hardness requirement—all NAAMS pins are hardened to 58–62 HRc for wear resistance in high-cycle production environments
Why standardize locating pins?
In automotive Body-in-White production, a single vehicle body may pass through dozens of welding, assembly, and inspection fixtures before completion. Each fixture uses locating pins to establish datum points that define part position in 3D space. If those pins are not consistent—in dimension, tolerance, or material—accumulated positioning errors result in poor panel fit-up, weld misalignment, and failed dimensional audits.
Before the NAAMS standard, each OEM and Tier 1 supplier maintained their own proprietary fixture component specifications. This created significant overhead: custom drawings for every pin, separate supplier qualifications, non-interchangeable replacement parts, and extended downtime when a pin failed and a replacement had to be custom-ordered.
The result is reduced tooling cost, faster fixture build and repair, and consistent part location across all production shifts and facilities—which directly supports dimensional quality and reduced scrap rates.
Round pins vs. diamond pins: constraint geometry
The most fundamental choice in locating pin selection is between a round (4-way) pin and a diamond (2-way) pin. The distinction is about how many degrees of lateral freedom each pin constrains, and it directly relates to the classical 3-2-1 locating principle used in fixture design.
- Circular head engages the hole in all radial directions
- Constrains the part in both X and Y (4 degrees of lateral freedom removed)
- Used as the primary datum pin—establishes the part’s position in the plane
- Requires close hole-to-pin fit to maximize accuracy
- Series: APQ (large head), APS (small head)
- Two opposing flats ground into the head reduce contact to two points
- Constrains in one axis only (2 degrees of freedom removed)
- Used as the secondary (clocking) pin—prevents rotation without overconstraining
- The flat clearance accommodates center-distance variation between holes
- Series: APE (slotted hole diamond)
NAAMS pin series: APQ, APS, APE, ARE, ARP
The NAAMS catalog organizes locating pins into series by head size, geometry, and application. Each series covers a defined diameter range and is available in standard, coated, and retractable variants.
The APQ series is the most widely used NAAMS locating pin in Body-in-White assembly fixtures. The large head (wider than the 15.98mm insert base) provides a generous contact surface, making it suitable for medium-to-heavy panel location in welding and assembly stations.
Diameter range: 8, 10, 13, 16, 18, 20, 25, 30, 35, and 40mm · Length range: 55.4–162.5mm · Retractable variant: suffix R in NAAMS code
The APS series has a head diameter smaller than the APQ—the shoulder is 22 or 25mm in diameter. Used where envelope space is tighter or where a smaller contact footprint is preferred. Suited for lighter-gauge panels and smaller datum hole diameters.
Diameter range: 6, 8, 10, 12, 13, 16, 19, and 25mm · Length range: 51.8–179.8mm · Retractable variant available
The APE series diamond pin is designed for slotted datum holes, providing 2-way constraint to prevent part rotation without restricting linear float along the slot axis. This accommodates stamped hole tolerance variation and center-distance variation between datum holes in real-world sheet metal parts.
Slot sizes: 6×12, 8×14, 10×16, 12×18, 13×19, 16×22, 19×25, and 25×31mm · Length range: 52.9–170.1mm · Retractable variants: suffix R and S
Respot pins are used in resistance spot welding fixtures where the pin must locate the part accurately for repeated weld cycles. The ARE series features a large head design suited to heavier structural panels. Retractable variants allow the pin to clear the part during loading.
The ARP series provides the same respot pin function as ARE in a smaller head diameter, for tighter weld fixture envelopes or lighter panel applications. The 25mm diameter ARP250M–ARP259M range covers the full metric respot pin specification.
| Series | Head type | Constraint | Diameter range | Primary use |
|---|---|---|---|---|
| APQ | Large, round | 4-way | 8–40mm | Primary datum, assembly & weld fixtures |
| APS | Small, round | 4-way | 6–25mm | Primary datum, lighter panels, tight envelopes |
| APE | Diamond, slotted | 2-way | 6–25mm (slot) | Secondary (clocking) datum, overconstrain prevention |
| ARE | Large, respot | 4-way | 25mm+ | Resistance welding fixture location |
| ARP | Small, respot | 4-way | 25mm | Resistance welding, tight envelope |
Retractable locating pins
A retractable locating pin can be mechanically withdrawn below the fixture surface to allow a part to be placed without dragging across the pin tip, then extended upward to locate the part after seating. This is critical in automated loading applications where robots place parts from above and pin engagement must be controlled sequentially.
- ▸Mechanism: all NAAMS retractable pins include a slotted hole designed for an 8mm socket head shoulder screw assembly—the shoulder screw acts as the actuation interface
- ▸Availability: retractable variants exist for APQ, APS, APE, ARE, and ARP series—indicated by suffix R in the NAAMS code
- ▸When to use: automated part loading cells, transfer lines with robotic part placement, weld fixtures where part removal direction conflicts with fixed pin geometry
- ▸When not needed: manual load/unload fixtures where the operator can tilt the part clear of the pin, or where hole-to-pin clearance is sufficient for axial part removal
Materials and coatings
Base materials
All NAAMS locating pins are hardened to 58–62 HRc. The standard material is ANSI 4140 steel for uncoated pins. Coated pins use A2 or D2 tool steel, which hold hardening more consistently through the coating process. M2 high-speed tool steel is also available for maximum hardness and wear resistance in the most demanding applications.
Coatings
| Property | Uncoated (4140 steel) | RDLC Coating |
|---|---|---|
| Surface hardness (HV) | ~700 (58–62 HRc substrate) | 6,000–7,000 |
| Coating thickness (µm) | — | 0.2–1.0 |
| CoF vs. steel, dry | ~0.4–0.6 | 0.15–0.2 |
| Aluminum galling resistance | Moderate | High (prevents cold welding) |
| Visual identification | Black oxide or bare steel | Iridescent rainbow finish |
| Internal test cycles (aluminum workpiece) | — | >700,000 |
For a full breakdown of RDLC coating performance data, hardness testing, and wear rate results vs. uncoated M2 steel and 52100 steel, see the RDLC Locating Pins Comparison Study white paper. For a comparison of RDLC vs. WSR (Weld Splatter Resistant) coating for welding fixture applications, see WSR Coating for Body-in-White Production.
Use cases by fixture type
Selection guide: choosing the right NAAMS locating pin
Use the following decision framework when specifying NAAMS locating pins for a new or replacement fixture:
- 01Determine the datum hole geometry. Round hole→APQ or APS. Slotted hole→APE (diamond). Welding application→ARE or ARP (respot).
- 02Select head size. Large head (APQ, ARE) for medium-to-heavy panels and standard fixture plates. Small head (APS, ARP) for tight envelope, lighter gauge, or smaller datum diameters (6–13mm).
- 03Apply the 4-way + 2-way rule. Use one round pin (APQ or APS) as the primary datum and one diamond pin (APE) as the secondary clocking datum. Do not use two round pins in the same part—this will overconstrain the part and cause stress or poor location repeatability when hole position varies.
- 04Decide on retractable vs. fixed. Fixed pins are simpler and more robust. Use retractable pins only when part load/unload geometry or robotic automation requires pin withdrawal.
- 05Select coating based on workpiece material. For steel workpieces in welding environments, consult WSR coating. For aluminum or mixed steel/aluminum workpieces, RDLC coating provides the best galling resistance and longest service life.
- 06No drawing required. Specify the NAAMS code directly on the fixture BOM. The code fully defines the pin—series, diameter, length, and coating—and any NAAMS-qualified supplier can fulfill it.
