Wrench size, across corners, flange diameter and thickness for inch hex flange nuts, serrated and smooth, #10 to 3/4″. ASME B18.2.2.
A flange nut is a hex nut with a wide round flange built onto its bottom, so it works as its own washer. The serrated type has teeth under the flange that bite the mating surface and resist loosening; the smooth type doesn’t. Both are the same size and take the same wrench.
Letters match the table columns: F across flats (the wrench), G across corners, B flange diameter, H thickness, K flange thickness.
| Size | Wrench F | F max / min | Corners G max / min | Flange B max / min | Thickness H max / min | Flange K min |
|---|---|---|---|---|---|---|
| #10 | 3/8″ | .375 / .365 | .433 / .416 | .500 / .480 | .219 / .203 | .03 |
| 1/4″ | 7/16″ | .438 / .428 | .505 / .488 | .594 / .574 | .236 / .222 | .04 |
| 5/16″ | 1/2″ | .500 / .489 | .577 / .557 | .680 / .660 | .283 / .268 | .04 |
| 3/8″ | 9/16″ | .562 / .551 | .650 / .628 | .750 / .728 | .347 / .330 | .04 |
| 7/16″ | 11/16″ | .688 / .675 | .794 / .768 | .937 / .910 | .395 / .375 | .04 |
| 1/2″ | 3/4″ | .750 / .736 | .866 / .840 | 1.031 / 1.000 | .458 / .437 | .05 |
| 5/8″ | 15/16″ | .938 / .922 | 1.083 / 1.051 | 1.281 / 1.248 | .569 / .545 | .05 |
| 3/4″ | 1-1/8″ | 1.125 / 1.088 | 1.299 / 1.240 | 1.500 / 1.460 | .675 / .627 | .06 |
Same sizes for serrated and smooth flange nuts, and the same wrench as a standard hex nut of the same size.
Serrated or smooth?
The teeth under a serrated flange press into the surface under them as the nut is tightened, which resists loosening. A smooth flange just spreads the load. Standard hex nuts are on the hex nut chart; more nut styles on Nut Types & When to Use Them.
Quick answers
- What size wrench fits a 3/8" flange nut?
- A 3/8″ hex flange nut takes a 9/16″ wrench.
- What wrench size goes with each flange nut size?
- #10 – 3/8″, 1/4″ – 7/16″, 5/16″ – 1/2″, 3/8″ – 9/16″, 7/16″ – 11/16″, 1/2″ – 3/4″, 5/8″ – 15/16″, 3/4″ – 1-1/8″.
- How big is the flange on a 1/2" flange nut?
- 1.000–1.031″ across (ASME B18.2.2).
- Are serrated and smooth flange nuts the same size?
- Yes — same across the flats, flange and thickness. The serrated one has teeth under the flange to resist loosening.