ASME B18.21.1 External Tooth Lock Washers — Inch Series (No. 3 – 1 1/4 in)
ASME B18.21.1 external tooth lock washer dimensions for inch-series screws — inside diameter, outside diameter and thickness per nominal size from No. 3 through 1 1/4 in, with the outward-facing tooth count the source prints, transcribed row-for-row.
Last updated: 2026-11
Specifications
The external tooth lock washer turns its hardened points outward: a ring of teeth that bite the mating surface around the fastener's bearing circle, holding both the screw and the washer against rotation. On the collected chart it runs No. 3 through 1 1/4 in — starting one size above the internal-tooth table's floor, a detail worth knowing when matching pairs — with ID, OD, thickness and tooth count per size. The outward geometry is the aggressive variant: teeth cutting into the base material give the strongest anti-rotation bite of the tooth family, which is why external rings are the default on stamped-metal chassis, terminal hardware and grounding hardware (the tooth bite also doubles as an electrical bond through paint and oxide films — a genuine second function on grounding lugs and EMI shields). The costs are symmetrical: the bite marks the mating surface (wrong for finished faces), needs bearing-area real estate (wrong under countersunk heads), and like all tooth rings it assumes through-hardened material — not tabulated by the collected chart, an RFQ line. On thin or soft substrate, the teeth can embed deeply enough to relax preload over time; that dynamic, not the tooth count, decides whether this is the right hardware for the joint.
| Standard | ASME B18.21.1 — external tooth lock washers, inch series |
|---|---|
| Size range | Nominal screw sizes No. 3 – 1 1/4 in, 19 printed rows (chart floor one size above the internal-tooth table) |
| Tabulated limits (in) | Per row: inside diameter max/min, outside diameter max/min, thickness max/min, plus teeth count as printed per size |
| Function | Outward-facing hardened teeth bite the mating surface around the bearing circle — strongest anti-rotation bite of the tooth family; also serves as an electrical bond through surface films on grounding hardware |
| Hardness / finish / material | Not tabulated by the collected chart — per RFQ; functional locking requires through-hardened material — state hardness and finish |
| Nominal Size (thread dia.) | A — Inside Dia. (max) | A (min) | B — Outside Dia. (max) | B (min) | C — Thickness (max) | C (min) |
|---|---|---|---|---|---|---|
| No.3 (0.099) | 0.109 | 0.102 | 0.235 | 0.220 | 0.016 | 0.010 |
| No.4 (0.112) | 0.123 | 0.115 | 0.260 | 0.245 | 0.018 | 0.012 |
| No.5 (0.125) | 0.136 | 0.129 | 0.285 | 0.270 | 0.020 | 0.014 |
| No.6 (0.138) | 0.150 | 0.141 | 0.320 | 0.305 | 0.022 | 0.016 |
| No.8 (0.164) | 0.176 | 0.168 | 0.381 | 0.365 | 0.023 | 0.018 |
| No.10 (0.190) | 0.204 | 0.195 | 0.410 | 0.395 | 0.024 | 0.018 |
| No.12 (0.216) | 0.231 | 0.221 | 0.475 | 0.460 | 0.027 | 0.020 |
| 1/4 (0.250) | 0.267 | 0.256 | 0.510 | 0.494 | 0.028 | 0.023 |
| 5/16 (0.3125) | 0.332 | 0.320 | 0.610 | 0.588 | 0.034 | 0.028 |
| 3/8 (0.375) | 0.398 | 0.384 | 0.694 | 0.670 | 0.040 | 0.032 |
| 7/16 (0.4375) | 0.464 | 0.448 | 0.760 | 0.740 | 0.040 | 0.032 |
| 1/2 (0.500) | 0.530 | 0.513 | 0.900 | 0.880 | 0.045 | 0.037 |
| 9/16 (0.5625) | 0.596 | 0.576 | 0.985 | 0.960 | 0.045 | 0.037 |
| 5/8 (0.625) | 0.663 | 0.641 | 1.070 | 1.045 | 0.050 | 0.042 |
| 11/16 (0.6875) | 0.728 | 0.704 | 1.155 | 1.130 | 0.050 | 0.042 |
| 3/4 (0.750) | 0.795 | 0.768 | 1.260 | 1.220 | 0.055 | 0.047 |
| 13/16 (0.8125) | 0.861 | 0.833 | 1.315 | 1.290 | 0.055 | 0.047 |
| 7/8 (0.875) | 0.927 | 0.897 | 1.410 | 1.380 | 0.060 | 0.052 |
| 1 (1.000) | 1.060 | 1.025 | 1.620 | 1.590 | 0.067 | 0.059 |
Materials
- Through-hardened spring steel or stainless is the functional requirement; note tooth bite marks finished surfaces — choose washer and substrate materials together at RFQ
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ASME B18.21.1 External Tooth Lock Washers — Inch Series (No. 3 – 1 1/4 in)) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
When should I choose external-tooth over internal-tooth or helical washers — and what are the trade-offs on finished surfaces?
Choose external teeth when anti-rotation is the priority and the mating surface can afford the bite. On stamped chassis, terminal blocks and grounding hardware, the outward ring locks screw and washer simultaneously and gives the strongest bite of the lock-washer family; on grounding and EMI hardware it does double duty, with the teeth penetrating paint and oxide to make electrical contact — a function the internal-tooth and helical types only partially provide. The trade-offs are physical: the teeth mark the surface (never under finished or painted faces where appearance or corrosion-start matters), they need the OD real estate (countersunk heads leave no room — that is internal-tooth territory), and on thin or soft substrate the points embed, relaxing preload over time — for that duty, a wide plain fender washer spreading load may hold better than any tooth ring. A sizing detail from the collected chart: the external-tooth table starts at No. 3 while the internal starts at No. 2, so a No. 2 screw pairs with internal only. As with all lock washers, hardness and material arrive at RFQ — a soft external ring neither bites nor bonds — and for high-preload or thermal-cycling joints, name an engineered locking method on the drawing instead of defaulting to hardware.
What is the MOQ and lead time for washers on this standard?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Common inch sizes are widely stocked; confirm the exact schedule against quantity and size mix at quotation.
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support