Wrench size and thickness for all-metal lock nuts: prevailing-torque (Grade C), top lock, two-way reversible and K-lock (Kep) nuts, by size.
An all-metal lock nut holds against vibration without a nylon ring. A prevailing-torque or top lock nut has its top threads squeezed out of round, so it grips the bolt as it turns on; a two-way reversible nut is squeezed in the middle, so either face can go on first; a K-lock (Kep) nut carries a free-spinning tooth washer that bites into the part. On every prevailing-torque, top lock, two-way and K-lock size below, the wrench is the same as a hex nut of that size (see our hex nut chart).
| Size | Wrench F | F max / min | Thickness H max / min |
|---|---|---|---|
| 1/4″ | 7/16″ | .438 / .428 | — / .212 |
| 5/16″ | 1/2″ | .502 / .489 | — / — |
| 3/8″ | 9/16″ | .564 / .551 | — / .320 |
| 7/16″ | 11/16″ | .689 / .675 | — / .365 |
| 1/2″ | 3/4″ | .752 / .736 | — / .427 |
| 9/16″ | 7/8″ | — / .861 | — / .473 |
| 5/8″ | 15/16″ | .939 / .922 | — / .535 |
| 3/4″ | 1-1/8″ | 1.127 / 1.088 | — / .617 |
| 7/8″ | 1-5/16″ | 1.314 / 1.269 | — / .724 |
| 1″ | 1-1/2″ | 1.502 / 1.450 | — / .831 |
| Size | Wrench F | F max / min | Thickness H max / min |
|---|---|---|---|
| 1/4″ | 7/16″ | .438 / .428 | .257 / .243 |
| 5/16″ | 1/2″ | — / .489 | .302 / .292 |
| 3/8″ | 9/16″ | — / .551 | .377 / .360 |
| 7/16″ | 11/16″ | — / .675 | .430 / .410 |
| 1/2″ | 3/4″ | — / .736 | .510 / .490 |
| 5/8″ | 15/16″ | — / .922 | .645 / .621 |
| 3/4″ | 1-1/8″ | — / 1.088 | .750 / .702 |
| 7/8″ | 1-5/16″ | — / 1.269 | .862 / .810 |
| 1″ | 1-1/2″ | — / 1.450 | .958 / .902 |
| Size | Wrench F | F max / min | Thickness H max / min |
|---|---|---|---|
| 1-1/8″ | 1-11/16″ | — / 1.631 | .999 / .939 |
| 1-1/4″ | 1-7/8″ | 1.875 / 1.812 | 1.094 / 1.030 |
| 1-3/8″ | 2-1/16″ | 2.062 / 1.994 | 1.206 / 1.138 |
| 1-1/2″ | 2-1/4″ | 2.250 / 2.175 | 1.317 / 1.245 |
| Size | Wrench F | F max / min | Thickness H max / min |
|---|---|---|---|
| 1/4″ | 7/16″ | .438 / .428 | .226 / .212 |
| 5/16″ | 1/2″ | — / .489 | .273 / .258 |
| 3/8″ | 9/16″ | — / .551 | .337 / .320 |
| 1/2″ | 3/4″ | — / .736 | .448 / .427 |
| 5/8″ | 15/16″ | — / .922 | .559 / .535 |
| 3/4″ | 1-1/8″ | — / 1.088 | .665 / .617 |
| 7/8″ | 1-5/16″ | — / 1.269 | .776 / .724 |
| 1″ | 1-1/2″ | — / 1.450 | .887 / .831 |
| Size | Wrench F | F max / min | Thickness H max / min |
|---|---|---|---|
| #8 | 11/32″ | .344 / .332 | — / — |
| #10 | 3/8″ | .375 / .362 | .203 / .187 |
| 1/4″ | 7/16″ | .438 / .428 | — / — |
| 5/16″ | 1/2″ | .500 / .489 | .273 / .258 |
| 3/8″ | 9/16″ | — / .551 | .337 / .320 |
| 7/16″ | 11/16″ | .688 / .675 | .385 / .365 |
| 1/2″ | 3/4″ | .750 / .736 | .448 / .427 |
| 9/16″ | 7/8″ | .875 / .861 | .496 / .473 |
| 5/8″ | 15/16″ | .938 / .922 | .559 / .535 |
| 3/4″ | 1-1/8″ | 1.125 / 1.088 | .665 / .617 |
| 7/8″ | 1-5/16″ | 1.312 / 1.269 | .776 / .724 |
| 1″ | 1-1/2″ | 1.500 / 1.450 | .887 / .831 |
| Size | Wrench F |
|---|---|
| #4 | 1/4″ |
| #6 | 5/16″ |
| #8 | 11/32″ |
| #10 | 3/8″ |
| 1/4″ | 7/16″ |
| 5/16″ | 1/2″ |
| 3/8″ | 9/16″ |
Good to know
Grade C lock nuts go with Grade 8 bolts. A Grade C prevailing-torque or top lock nut is the all-metal lock nut made for Grade 8 strength; all-metal lock nuts also take heat (up to about 450°F) that a nylon ring can’t.
Grade B lock nuts go with Grade 5 bolts. Use a Grade B prevailing-torque nut with a Grade 5 bolt (RB&W and Alma both say so); a Grade 8 bolt takes Grade C.
Two-way nuts lock in the middle. A two-way reversible nut grips the bolt in the center of its threads, so it can go on either face first and the bolt doesn’t have to stick out past the nut to lock.
Top lock nuts are hex nut size. On this chart a top lock nut has the same wrench and the same thickness as a hex nut of its size, so it fits wherever the hex nut did.
A K-lock grips the part, not the bolt. Its tooth washer bites into the surface as the nut is tightened, so it locks only against a surface the teeth can dig into.
Quick answers
- What size wrench fits a 3/8 lock nut?
- A 3/8″ all-metal lock nut (prevailing-torque, top lock or two-way) takes a 9/16″ wrench, the same as a 3/8″ hex nut.
- What size socket for a 1/2-13 top lock nut?
- 3/4″. A 1/2″ top lock nut is 0.427″ to 0.448″ thick.
- What wrench fits a 1/4 Kep nut?
- A 1/4″ K-lock (Kep) nut takes a 7/16″ wrench; a #10 takes 3/8″.
- What is a two-way reversible lock nut?
- An all-metal lock nut squeezed in the middle of its threads, so it locks with either face down. A 5/8″ one takes a 15/16″ wrench.
- What bolt goes with a Grade C lock nut?
- A Grade 8 bolt. Grade C is the all-metal lock nut grade made for Grade 8 strength.