Wrench size, height and thread depth for low crown acorn (cap) nuts, #6 to 3/4″, and the wrench for high crown acorn nuts. SAE J483.
An acorn nut is a hex nut closed off with a domed top. It covers the end of the bolt — for looks, and to cover the projecting threads. Because the top is closed, the bolt can only go in so far: check the thread depth before you pick the bolt length.
Letters match the table columns: F across flats (the wrench), H overall height, Q hex height, U full thread depth, T drill depth.
| Size | Wrench F | F max / min | Corners G max / min | Height H | Hex height Q | Full thread U | Drill depth T |
|---|---|---|---|---|---|---|---|
| #6 | 5/16″ | .3125 / .302 | .361 / .344 | .34 | .16 | .16 | .25 |
| #8 | 5/16″ | .3125 / .302 | .361 / .344 | .34 | .16 | .16 | .25 |
| #10 | 3/8″ | .3750 / .362 | .433 / .413 | .41 | .19 | .19 | .28 |
| 1/4″ | 7/16″ | .4375 / .428 | .505 / .488 | .47 | .22 | .25 | .34 |
| 5/16″ | 1/2″ | .5000 / .489 | .577 / .557 | .53 | .25 | .31 | .41 |
| 3/8″ | 9/16″ | .5625 / .551 | .650 / .628 | .62 | .28 | .38 | .45 |
| 1/2″ | 3/4″ | .7500 / .736 | .866 / .840 | .81 | .38 | .50 | .59 |
| 5/8″ | 15/16″ | .9375 / .922 | 1.083 / 1.051 | 1.00 | .47 | .62 | .75 |
| 3/4″ | 1-1/16″ | 1.0625 / 1.045 | 1.227 / 1.191 | 1.16 | .53 | .75 | .88 |
Heights and depths are nominal. The bolt should end inside the full thread (U); past it, it bottoms in the drilled hole.
| Size | Wrench F | F max / min |
|---|---|---|
| 1/4″ | 7/16″ | — |
| 5/16″ | 1/2″ | — |
| 3/8″ | 9/16″ | — |
| 7/16″ | 5/8″ | — |
| 1/2″ | 3/4″ | — |
| 9/16″ | 7/8″ | .8750 / .861 |
A high crown acorn nut takes the same wrench as a low crown nut of its size; its dome is taller. Its height and thread depth: only one of our sources lists them — give us a call. A dash: our sources differ, or only one lists it.
What they’re for
Acorn nuts are used as decorative pieces and as covers for projecting threads. Other nut styles are on Nut Types & When to Use Them; standard hex nuts on the hex nut chart.
Quick answers
- What size wrench fits a 3/8" acorn nut?
- A 3/8″ acorn nut takes a 9/16″ wrench (low or high crown).
- What wrench size goes with each acorn nut size?
- #6 – 5/16″, #8 – 5/16″, #10 – 3/8″, 1/4″ – 7/16″, 5/16″ – 1/2″, 3/8″ – 9/16″, 1/2″ – 3/4″, 5/8″ – 15/16″, 3/4″ – 1-1/16″ (low crown, SAE J483).
- How deep is the thread in a 1/2" acorn nut?
- Full thread .50″ deep, drilled .59″ (low crown). The bolt should end inside the full thread.
- How tall is a 1/4" acorn nut?
- .47″ overall (low crown, SAE J483).
- What wrench fits a 7/16 high crown acorn nut?
- A 5/8″ wrench.