Hole, outside diameter, thickness and width for regular split lock washers, #2 to 1-1/2″ — by the bolt they fit. ASME B18.21.1.
A split lock washer is a hardened spring ring with one cut in it, sized by the bolt it fits: a ½″ lock washer goes on a ½″ bolt. The regular series below is the everyday one; heavy, extra-duty and hi-collar versions of the same size are thicker or narrower.
Letters match the table columns: ID the hole, OD across the outside, T thickness and W width of the ring’s section.
| Bolt size | Hole ID max / min | Outside OD max | Thickness T min | Width W min |
|---|---|---|---|---|
| #2 | .094 / .088 | .172 | .020 | .035 |
| #4 | .120 / .114 | .209 | .025 | .040 |
| #5 | .133 / .127 | .236 | .031 | .047 |
| #6 | .148 / .141 | .250 | .031 | .047 |
| #8 | .174 / .167 | .293 | .040 | .055 |
| #10 | .200 / .193 | .334 | .047 | .062 |
| #12 | .227 / .220 | .377 | .056 | .070 |
| 1/4″ | .260 / .252 | .487 | .062 | .109 |
| 5/16″ | .322 / .314 | .583 | .078 | .125 |
| 3/8″ | .385 / .377 | .680 | .094 | .141 |
| 7/16″ | .450 / .440 | .776 | .109 | .156 |
| 1/2″ | .512 / .502 | .869 | .125 | .171 |
| 9/16″ | .574 / .564 | .965 | .141 | .188 |
| 5/8″ | .641 / .628 | 1.073 | .156 | .203 |
| 3/4″ | .766 / .753 | 1.265 | .188 | .234 |
| 7/8″ | .894 / .878 | 1.459 | .219 | .266 |
| 1″ | 1.024 / 1.003 | 1.656 | .250 | .297 |
| 1-1/8″ | 1.153 / 1.129 | 1.847 | .281 | .328 |
| 1-1/4″ | 1.280 / 1.254 | 2.036 | .312 | .359 |
| 1-3/8″ | 1.408 / 1.379 | 2.219 | .344 | .391 |
| 1-1/2″ | 1.534 / 1.504 | 2.419 | .375 | .422 |
Regular series. Thickness is the mean of the section’s inside and outside edges. Steel and stainless are made to the same sizes. High-alloy lock washers (4037 alloy steel, for grade 5 and grade 8 bolts) are made to the same sizes through 1″.
| Size | Hole ID max / min | OD max | Thickness min | Width min |
|---|---|---|---|---|
| #4 | .120 / .114 | .173 | .022 | .022 |
| #6 | .148 / .141 | .216 | .030 | .030 |
| #8 | .174 / .167 | .267 | .047 | .042 |
| #10 | .200 / .193 | .294 | .047 | .042 |
| 1/4″ | .260 / .252 | .363 | .078 | .047 |
| 5/16″ | .322 / .314 | .457 | .093 | .062 |
| 3/8″ | .385 / .377 | .550 | .125 | .076 |
| 7/16″ | .450 / .440 | .644 | .140 | .090 |
| 1/2″ | .512 / .502 | .733 | .172 | .103 |
| 5/8″ | .641 / .628 | .917 | .203 | .125 |
| 3/4″ | .766 / .753 | 1.105 | .218 | .154 |
| 7/8″ | .894 / .878 | 1.291 | .234 | .182 |
| 1″ | 1.024 / 1.003 | 1.478 | .250 | .208 |
| 1-1/8″ | 1.153 / 1.129 | 1.663 | .313 | .236 |
| 1-1/4″ | 1.280 / 1.254 | 1.790 | .313 | .236 |
| 1-1/2″ | 1.534 / 1.504 | 2.159 | .375 | .292 |
Hi-collar lock washers are thicker, with a smaller outside diameter than a regular split lock washer, for socket head cap screws and other small heads.
| Size | Hole ID max / min | OD max / min | Thickness max / min |
|---|---|---|---|
| #2 | .095 / .089 | .200 / .175 | .016 / .010 |
| #3 | .109 / .102 | .232 / .215 | .016 / .010 |
| #4 | .123 / .115 | .270 / .245 | .018 / .012 |
| #5 | .136 / .129 | .280 / .255 | .020 / .014 |
| #6 | .150 / .141 | .295 / .275 | .022 / .016 |
| #8 | .176 / .168 | .340 / .325 | .023 / .018 |
| #10 | .204 / .195 | .381 / .365 | .024 / .018 |
| #12 | .231 / .221 | .410 / .394 | .027 / .020 |
| 1/4″ | .267 / .256 | .478 / .460 | .028 / .023 |
| 5/16″ | .332 / .320 | .610 / .594 | .034 / .028 |
| 3/8″ | .398 / .384 | .692 / .670 | .040 / .032 |
| 7/16″ | .464 / .448 | .789 / .740 | .040 / .032 |
| 1/2″ | .530 / .512 | .900 / .867 | .045 / .037 |
| 9/16″ | .596 / .576 | .985 / .957 | .045 / .037 |
| 5/8″ | .663 / .640 | 1.071 / 1.045 | .050 / .042 |
| 3/4″ | .795 / .769 | 1.245 / 1.220 | .055 / .047 |
| 7/8″ | .927 / .894 | 1.410 / 1.364 | .060 / .052 |
| 1″ | 1.060 / 1.019 | 1.637 / 1.590 | .067 / .059 |
| 1-1/8″ | 1.192 / 1.144 | 1.830 / 1.799 | .067 / .059 |
| 1-1/4″ | 1.325 / 1.275 | 1.975 / 1.921 | .067 / .059 |
Internal tooth lock washers have their teeth on the inside edge, hidden under the head — the pick for small heads such as fillister screws.
| Size | Hole ID max / min | OD max / min | Thickness max / min |
|---|---|---|---|
| #3 | .109 / .102 | .235 / .220 | .016 / .010 |
| #4 | .123 / .115 | .260 / .245 | .018 / .012 |
| #5 | .136 / .129 | .285 / .270 | .020 / .014 |
| #6 | .150 / .141 | .320 / .305 | .022 / .016 |
| #8 | .176 / .168 | .381 / .365 | .023 / .018 |
| #10 | .204 / .195 | .410 / .395 | .024 / .018 |
| #12 | .231 / .221 | .475 / .460 | .027 / .020 |
| 1/4″ | .267 / .256 | .510 / .494 | .028 / .023 |
| 5/16″ | .332 / .320 | .610 / .588 | .034 / .028 |
| 3/8″ | .398 / .384 | .694 / .670 | .040 / .032 |
| 7/16″ | .464 / .448 | .760 / .740 | .040 / .032 |
| 1/2″ | .530 / .513 | .900 / .880 | .045 / .037 |
| 9/16″ | .596 / .576 | .985 / .960 | .045 / .037 |
| 5/8″ | .663 / .641 | 1.070 / 1.045 | .050 / .042 |
| 3/4″ | .795 / .768 | 1.260 / 1.220 | .055 / .047 |
| 7/8″ | .927 / .897 | 1.410 / 1.380 | .060 / .052 |
| 1″ | 1.060 / 1.025 | 1.620 / 1.590 | .067 / .059 |
External tooth lock washers have their teeth on the outside edge — the most grip, since the teeth sit on the largest radius.
How to measure a lock washer
Measure the hole and across the outside, then find the row they fit. The bolt size on that row is the washer’s size. A washer much thicker than the table is a heavy or extra-duty one; a narrow, thick one is a hi-collar.
Do lock washers work?
A split lock washer helps resist loosening from light vibration. For serious vibration, a lock nut or threadlocker does more — see Washer Types & When to Use Them and the flat washer chart.
Quick answers
- What size is a 1/2" lock washer?
- A regular 1/2″ split lock washer has a .502–.512″ hole, is .869″ across at most and .125″ thick (minimum).
- What is the outside diameter of a 3/8" split lock washer?
- .680″ maximum (regular series, ASME B18.21.1).
- How thick is a 1/4" lock washer?
- .062″ minimum, with a ring .109″ wide (regular series).
- Do split lock washers stop bolts from loosening?
- They help against light vibration. For serious vibration, a lock nut or threadlocker does more.