Across flats, across corners and thickness for inch hex nuts, heavy hex nuts and hex jam nuts — with the wrench size for each. ASME B18.2.2.
A nut is sized by the bolt it fits: a ½″ nut goes on a ½″ bolt. The numbers below are the nut itself. Across flats is your wrench size; across corners is the room it needs to turn; thickness is how much thread it grips. Standard hex, heavy hex and jam nuts of the same size are three different nuts — check which one you have.
Letters match the table columns. F across flats (the wrench size), G across corners, H thickness.
| Size | Across flats F (wrench) | F max / min | Across corners G max / min | Thickness H | H max / min |
|---|---|---|---|---|---|
| 1/4″ | 7/16″ | .438 / .428 | .505 / .488 | 7/32″ | .226 / .212 |
| 5/16″ | 1/2″ | .500 / .489 | .577 / .557 | 17/64″ | .273 / .258 |
| 3/8″ | 9/16″ | .562 / .551 | .650 / .628 | 21/64″ | .337 / .320 |
| 7/16″ | 11/16″ | .688 / .675 | .794 / .768 | 3/8″ | .385 / .365 |
| 1/2″ | 3/4″ | .750 / .736 | .866 / .840 | 7/16″ | .448 / .427 |
| 9/16″ | 7/8″ | .875 / .861 | 1.010 / .982 | 31/64″ | .496 / .473 |
| 5/8″ | 15/16″ | .938 / .922 | 1.083 / 1.051 | 35/64″ | .559 / .535 |
| 3/4″ | 1-1/8″ | 1.125 / 1.088 | 1.299 / 1.240 | 41/64″ | .665 / .617 |
| 7/8″ | 1-5/16″ | 1.312 / 1.269 | 1.516 / 1.447 | 3/4″ | .776 / .724 |
| 1″ | 1-1/2″ | 1.500 / 1.450 | 1.732 / 1.653 | 55/64″ | .887 / .831 |
| 1-1/8″ | 1-11/16″ | 1.688 / 1.631 | 1.949 / 1.859 | 31/32″ | .999 / .939 |
| 1-1/4″ | 1-7/8″ | 1.875 / 1.812 | 2.165 / 2.066 | 1-1/16″ | 1.094 / 1.030 |
| 1-3/8″ | 2-1/16″ | 2.062 / 1.994 | 2.382 / 2.273 | 1-11/64″ | 1.206 / 1.138 |
| 1-1/2″ | 2-1/4″ | 2.250 / 2.175 | 2.598 / 2.480 | 1-9/32″ | 1.317 / 1.245 |
The everyday hex nut. Same wrench as a hex cap screw of the same size except 7/16″ (11/16″) and 9/16″ (7/8″), where the nut is one size bigger.
| Size | Across flats F (wrench) | F max / min | Across corners G max / min | Thickness H | H max / min |
|---|---|---|---|---|---|
| 1/4″ | 1/2″ | .500 / .488 | .577 / .556 | 15/64″ | .250 / .218 |
| 5/16″ | 9/16″ | .562 / .546 | .650 / .622 | 19/64″ | .314 / .280 |
| 3/8″ | 11/16″ | .688 / .669 | .794 / .763 | 23/64″ | .377 / .341 |
| 7/16″ | 3/4″ | .750 / .728 | .866 / .830 | 27/64″ | .441 / .403 |
| 1/2″ | 7/8″ | .875 / .850 | 1.010 / .969 | 31/64″ | .504 / .464 |
| 9/16″ | 15/16″ | .938 / .909 | 1.083 / 1.037 | 35/64″ | .568 / .526 |
| 5/8″ | 1-1/16″ | 1.062 / 1.031 | 1.227 / 1.175 | 39/64″ | .631 / .587 |
| 3/4″ | 1-1/4″ | 1.250 / 1.212 | 1.443 / 1.382 | 47/64″ | .758 / .710 |
| 7/8″ | 1-7/16″ | 1.438 / 1.394 | 1.660 / 1.589 | 55/64″ | .885 / .833 |
| 1″ | 1-5/8″ | 1.625 / 1.575 | 1.876 / 1.796 | 63/64″ | 1.012 / .956 |
| 1-1/8″ | 1-13/16″ | 1.812 / 1.756 | 2.093 / 2.002 | 1-7/64″ | 1.139 / 1.079 |
| 1-1/4″ | 2″ | 2.000 / 1.938 | 2.309 / 2.209 | 1-7/32″ | 1.251 / 1.187 |
| 1-3/8″ | 2-3/16″ | 2.188 / 2.119 | 2.526 / 2.416 | 1-11/32″ | 1.378 / 1.310 |
| 1-1/2″ | 2-3/8″ | 2.375 / 2.300 | 2.742 / 2.622 | 1-15/32″ | 1.505 / 1.433 |
| 1-5/8″ | 2-9/16″ | 2.562 / 2.481 | 2.959 / 2.828 | 1-19/32″ | 1.632 / 1.556 |
| 1-3/4″ | 2-3/4″ | 2.750 / 2.662 | 3.175 / 3.035 | 1-23/32″ | 1.759 / 1.679 |
| 2″ | 3-1/8″ | 3.125 / 3.025 | 3.608 / 3.449 | 1-31/32″ | 2.013 / 1.925 |
| 2-1/4″ | 3-1/2″ | 3.500 / 3.388 | 4.041 / 3.862 | 2-13/64″ | 2.251 / 2.155 |
| 2-1/2″ | 3-7/8″ | 3.875 / 3.750 | 4.474 / 4.275 | 2-29/64″ | 2.505 / 2.401 |
| 2-3/4″ | 4-1/4″ | 4.250 / 4.112 | 4.907 / 4.688 | 2-45/64″ | 2.759 / 2.647 |
| 3″ | 4-5/8″ | 4.625 / 4.475 | 5.340 / 5.102 | 2-61/64″ | 3.013 / 2.893 |
| 3-1/4″ | 5″ | 5.000 / 4.838 | 5.774 / 5.515 | 3-3/16″ | 3.252 / 3.124 |
| 3-1/2″ | 5-3/8″ | 5.375 / 5.200 | 6.207 / 5.928 | 3-7/16″ | 3.506 / 3.370 |
| 3-3/4″ | 5-3/4″ | 5.750 / 5.562 | 6.640 / 6.341 | 3-11/16″ | 3.760 / 3.616 |
| 4″ | 6-1/8″ | 6.125 / 5.925 | 7.073 / 6.755 | 3-15/16″ | 4.014 / 3.862 |
One size wider across the flats and thicker than a standard nut — the nut for structural and high-strength bolting (A325, A490, B7 studs). See the nut compatibility chart.
| Size | Across flats F (wrench) | Thickness H | H max / min |
|---|---|---|---|
| 1/4″ | 7/16″ | 5/32″ | .163 / .150 |
| 5/16″ | 1/2″ | 3/16″ | .195 / .180 |
| 3/8″ | 9/16″ | 7/32″ | .227 / .210 |
| 7/16″ | 11/16″ | 1/4″ | .260 / .240 |
| 1/2″ | 3/4″ | 5/16″ | .323 / .302 |
| 9/16″ | 7/8″ | 5/16″ | .324 / .301 |
| 5/8″ | 15/16″ | 3/8″ | .387 / .363 |
| 3/4″ | 1-1/8″ | 27/64″ | .446 / .398 |
| 7/8″ | 1-5/16″ | 31/64″ | .510 / .458 |
| 1″ | 1-1/2″ | 35/64″ | .575 / .519 |
| 1-1/8″ | 1-11/16″ | 39/64″ | .639 / .579 |
| 1-1/4″ | 1-7/8″ | 23/32″ | .751 / .687 |
| 1-3/8″ | 2-1/16″ | 25/32″ | .815 / .747 |
| 1-1/2″ | 2-1/4″ | 27/32″ | .880 / .808 |
A thin hex nut: same across flats and corners as the standard hex nut above, a little over half as thick. Run against a second nut to lock it, or use where a full nut won’t fit.
| Size | Across flats F (wrench) | Thickness H | H max / min |
|---|---|---|---|
| 1/4″ | 1/2″ | 11/64″ | .188 / .156 |
| 5/16″ | 9/16″ | 13/64″ | .220 / .186 |
| 3/8″ | 11/16″ | 15/64″ | .252 / .216 |
| 7/16″ | 3/4″ | 17/64″ | .285 / .247 |
| 1/2″ | 7/8″ | 19/64″ | .317 / .277 |
| 9/16″ | 15/16″ | 21/64″ | .349 / .307 |
| 5/8″ | 1-1/16″ | 23/64″ | .381 / .337 |
| 3/4″ | 1-1/4″ | 27/64″ | .446 / .398 |
| 7/8″ | 1-7/16″ | 31/64″ | .510 / .458 |
| 1″ | 1-5/8″ | 35/64″ | .575 / .519 |
| 1-1/8″ | 1-13/16″ | 39/64″ | .639 / .579 |
| 1-1/4″ | 2″ | 23/32″ | .751 / .687 |
| 1-3/8″ | 2-3/16″ | 25/32″ | .815 / .747 |
| 1-1/2″ | 2-3/8″ | 27/32″ | .880 / .808 |
| 1-5/8″ | 2-9/16″ | 29/32″ | .944 / .868 |
| 1-3/4″ | 2-3/4″ | 31/32″ | 1.009 / .929 |
| 2″ | 3-1/8″ | 1-3/32″ | 1.138 / 1.050 |
| 2-1/4″ | 3-1/2″ | 1-13/64″ | 1.251 / 1.155 |
| 2-1/2″ | 3-7/8″ | 1-29/64″ | 1.505 / 1.401 |
| 2-3/4″ | 4-1/4″ | 1-37/64″ | 1.634 / 1.522 |
| 3″ | 4-5/8″ | 1-45/64″ | 1.763 / 1.643 |
| 3-1/4″ | 5″ | 1-13/16″ | 1.876 / 1.748 |
| 3-1/2″ | 5-3/8″ | 1-15/16″ | 2.006 / 1.870 |
| 3-3/4″ | 5-3/4″ | 2-1/16″ | 2.134 / 1.990 |
| 4″ | 6-1/8″ | 2-3/16″ | 2.264 / 2.112 |
A thin heavy hex nut: same across flats and corners as the heavy hex nut above. Run against a heavy hex nut to lock it.
| Size | Across flats F (wrench) | Thickness H | Unslotted T max / min | Slot width S max / min |
|---|---|---|---|---|
| 1/4″ | 7/16″ | 7/32″ | .14 / .12 | .10 / .07 |
| 5/16″ | 1/2″ | 17/64″ | .18 / .16 | .12 / .09 |
| 3/8″ | 9/16″ | 21/64″ | .21 / .19 | .15 / .12 |
| 7/16″ | 11/16″ | 3/8″ | .23 / .21 | .15 / .12 |
| 1/2″ | 3/4″ | 7/16″ | .29 / .27 | .18 / .15 |
| 9/16″ | 7/8″ | 31/64″ | .31 / .29 | .18 / .15 |
| 5/8″ | 15/16″ | 35/64″ | .34 / .32 | .24 / .18 |
| 3/4″ | 1-1/8″ | 41/64″ | .40 / .38 | .24 / .18 |
| 7/8″ | 1-5/16″ | 3/4″ | .52 / .49 | .24 / .18 |
| 1″ | 1-1/2″ | 55/64″ | .59 / .56 | .30 / .24 |
| 1-1/8″ | 1-11/16″ | 31/32″ | .64 / .61 | .33 / .24 |
| 1-1/4″ | 1-7/8″ | 1-1/16″ | .70 / .67 | .40 / .31 |
| 1-3/8″ | 2-1/16″ | 1-11/64″ | .82 / .78 | .40 / .31 |
| 1-1/2″ | 2-1/4″ | 1-9/32″ | .86 / .82 | .46 / .37 |
A standard hex nut with three slots across the top for a cotter pin. Same wrench, corners and thickness as the hex nut; T is the solid part under the slots.
| Size | Across flats F (wrench) | Thickness H | Unslotted T max / min | Slot width S max / min |
|---|---|---|---|---|
| 1/2″ | 7/8″ | 31/64″ | .34 / .32 | .18 / .15 |
| 5/8″ | 1-1/16″ | 39/64″ | .40 / .38 | .24 / .18 |
| 3/4″ | 1-1/4″ | 47/64″ | .49 / .47 | .24 / .18 |
| 7/8″ | 1-7/16″ | 55/64″ | .62 / .59 | .24 / .18 |
| 1″ | 1-5/8″ | 63/64″ | .72 / .69 | .30 / .24 |
| 1-1/8″ | 1-13/16″ | 1-7/64″ | .78 / .75 | .33 / .24 |
| 1-1/4″ | 2″ | 1-7/32″ | .86 / .83 | .40 / .31 |
| 1-3/8″ | 2-3/16″ | 1-11/32″ | .99 / .95 | .40 / .31 |
| 1-1/2″ | 2-3/8″ | 1-15/32″ | 1.05 / 1.01 | .46 / .37 |
The heavy hex nut, slotted. 1/2″ to 1-1/2″ — the sizes both our sources list.
| Nut grade | Sizes | UNC and 8UN | UNF |
|---|---|---|---|
| Grade 2 | 1/4 – 1-1/2″ | 90,000 | — |
| Grade 5 | 1/4 – 1″ | 120,000 | 109,000 |
| Grade 5 | over 1 – 1-1/2″ | 105,000 | 94,000 |
| Grade 8 | 1/4 – 1-1/2″ | 150,000 | 150,000 |
For standard (finished) hex nuts. A nut’s proof load in pounds = this stress × the thread’s tensile stress area (on the hex cap screw chart). Jam, slotted, castle and heavy nuts are rated differently. A dash: only one of our sources lists it — give us a call at 405-670-1234.
| Size | Flats F (wrench) | F max / min | Corners G max / min | Thickness H | H max / min | Unslotted T max / min | Slot S max / min |
|---|---|---|---|---|---|---|---|
| 1/4″ | 7/16″ | .438 / .428 | .505 / .488 | 9/32″ | .288 / .274 | .20 / .18 | .10 / .07 |
| 5/16″ | 1/2″ | .500 / .489 | .577 / .557 | 21/64″ | .336 / .320 | .24 / .22 | .12 / .09 |
| 3/8″ | 9/16″ | .562 / .551 | .650 / .628 | 13/32″ | .415 / .398 | .29 / .27 | .15 / .12 |
| 7/16″ | 11/16″ | .688 / .675 | .794 / .768 | 29/64″ | .463 / .444 | .31 / .29 | .15 / .12 |
| 1/2″ | 3/4″ | .750 / .736 | .866 / .840 | 9/16″ | .573 / .552 | .42 / .40 | .18 / .15 |
| 9/16″ | 7/8″ | .875 / .861 | 1.010 / .982 | 39/64″ | .621 / .598 | .43 / .41 | .18 / .15 |
| 5/8″ | 15/16″ | .938 / .922 | 1.083 / 1.051 | 23/32″ | .731 / .706 | .51 / .49 | .24 / .18 |
| 3/4″ | 1-1/8″ | 1.125 / 1.088 | 1.299 / 1.240 | 13/16″ | .827 / .798 | .57 / .55 | .24 / .18 |
| 7/8″ | 1-5/16″ | 1.312 / 1.269 | 1.516 / 1.447 | 29/32″ | .922 / .890 | .67 / .64 | .24 / .18 |
| 1″ | 1-1/2″ | 1.500 / 1.450 | 1.732 / 1.653 | 1″ | 1.018 / .982 | .73 / .70 | .30 / .24 |
| 1-1/4″ | 1-7/8″ | 1.875 / 1.812 | 2.165 / 2.066 | 1-1/4″ | 1.272 / 1.228 | .89 / .86 | .40 / .31 |
A thick hex nut with a round crown on top, slotted for a cotter pin. Same wrench as a standard hex nut, taller; T is the solid part under the slots.
| Size | Across flats F (wrench) | F max / min | Thickness H | H max / min |
|---|---|---|---|---|
| #0 | 5/32″ | .156 / .150 | 3/64″ | .050 / .043 |
| #1 | 5/32″ | .156 / .150 | 3/64″ | .050 / .043 |
| #2 | 3/16″ | .188 / .180 | 1/16″ | .066 / .057 |
| #3 | 3/16″ | .188 / .180 | 1/16″ | .066 / .057 |
| #4 | 1/4″ | .250 / .241 | 3/32″ | .098 / .087 |
| #5 | 5/16″ | — / — | 7/64″ | — / — |
| #6 | 5/16″ | .312 / .302 | 7/64″ | .114 / .102 |
| #8 | 11/32″ | — / .332 | 1/8″ | .130 / .117 |
| #10 | 3/8″ | .375 / .362 | 1/8″ | .130 / .117 |
| #12 | 7/16″ | .438 / .423 | 5/32″ | .161 / .148 |
| 1/4″ | 7/16″ | .438 / .423 | 3/16″ | .193 / .178 |
| 5/16″ | 9/16″ | .562 / .545 | 7/32″ | .225 / .208 |
| 3/8″ | 5/8″ | .625 / .607 | 1/4″ | .257 / .239 |
The small hex nut for machine screws, #0 to 3/8″. At 1/4″ and up it is thinner than a finished hex nut, and narrower at 5/16″ and 3/8″. A dash: our sources differ — give us a call at 405-670-1234.
Which nut do I have?
Measure across the flats and compare with the bolt size: a ½″ nut that takes a 3/4″ wrench is a standard hex; 7/8″ is a heavy hex. A nut noticeably thinner than the table’s standard thickness is a jam nut. More nut styles on Nut Types & When to Use Them; which grade of nut goes on which bolt is on the nut compatibility chart; bolt heads are on the hex cap screw dimensions chart.
Quick answers
- What size wrench fits a 1/2" hex nut?
- A 1/2″ hex nut takes a 3/4″ wrench. A 1/2″ heavy hex nut takes 7/8″.
- What wrench size goes with each hex nut size?
- Across the flats (the wrench): 1/4″ nut – 7/16″, 5/16″ nut – 1/2″, 3/8″ nut – 9/16″, 7/16″ nut – 11/16″, 1/2″ nut – 3/4″, 9/16″ nut – 7/8″, 5/8″ nut – 15/16″, 3/4″ nut – 1-1/8″, 7/8″ nut – 1-5/16″, 1″ nut – 1-1/2″, 1-1/8″ nut – 1-11/16″, 1-1/4″ nut – 1-7/8″, 1-3/8″ nut – 2-1/16″, 1-1/2″ nut – 2-1/4″.
- Is a heavy hex nut bigger than a regular hex nut?
- Yes — wider across the flats and thicker. A 3/4″ hex nut is 1-1/8″ across and 41/64″ thick; a 3/4″ heavy hex nut is 1-1/4″ across and 47/64″ thick.
- How thick is a jam nut?
- Thinner than a regular hex nut, same wrench. A 1/2″ jam nut is 5/16″ thick against 7/16″ for a regular 1/2″ hex nut.
- What is the proof load of a Grade 8 nut?
- SAE J995 Grade 8 hex nuts carry a proof load stress of 150,000 psi, coarse or fine thread, 1/4″ to 1-1/2″. Multiply by the thread’s stress area for pounds.