9/16-24 UNEF Thread Dimensions and Tap Drill
9/16-24 UNEF is the Unified extra fine thread for the 9/16 in (14.29 mm) diameter: 24 threads per inch, a pitch of 0.04167 in (1.058 mm), on a 60° profile. ASME B1.1 lists it in the UNEF series. Against the coarse 9/16-12 UNC it has 24 threads per inch instead of 12, a stress area 18% larger and a lead angle of 1.42° instead of 2.99°.
- Tap drill33/64"87% thread, 13.10 mm
- Pitch24 TPI1.058 mm
- Major diameter0.5625 in14.287 mm
- Pitch diameter0.5354 in13.600 mm
- Minor diameter (nut)0.5174 in13.142 mm
- Tensile stress area0.214 in²138 mm²
Thread profile
9/16-24 UNEF basic dimensions
| Dimension | in | mm |
|---|---|---|
| Major diameter d = D | 0.5625 | 14.287 |
| Pitch P | 0.04167 | 1.058 |
| Pitch diameter d2 = D2 | 0.5354 | 13.600 |
| Minor diameter, internal thread D1 | 0.5174 | 13.142 |
| Minor diameter, external UNR thread d3 | 0.5129 | 13.027 |
| Height of fundamental triangle H | 0.0361 | 0.917 |
| Thread height, internal (5H/8) | 0.0226 | 0.573 |
| Thread height, external (11H/16) | 0.0248 | 0.630 |
| Crest flat of external thread (P/8) | 0.0052 | 0.132 |
| Crest flat of internal thread (P/4) | 0.0104 | 0.265 |
| Property | Value |
|---|---|
| Threads per inch | 24 |
| Flank angle | 60° (30° each side) |
| Lead angle at the pitch diameter | 1.42° |
| Tensile stress area As | 0.214 in² (138 mm²) |
Basic (nominal) sizes per ASME B1.1, before tolerances. A UN external thread with a flat root has the same basic minor diameter as the nut (D1); d3 applies to the rounded UNR root.
9/16-24 UNEF limits of size (class 2A bolt, 2B nut)
Classes 2A and 2B are the general-purpose fits for commercial bolts, screws and nuts. The 2A external thread has an allowance of 0.0012 in, so its maximum size is that much below basic; the 2B nut starts at the basic size.
| External thread 2A | Max (in) | Min (in) | Tolerance (in) |
|---|---|---|---|
| Major diameter | 0.5613 | 0.5541 | 0.0072 |
| Pitch diameter | 0.5342 | 0.5302 | 0.0040 |
| Internal thread 2B | Max (in) | Min (in) | Tolerance (in) |
|---|---|---|---|
| Minor diameter | 0.527 | 0.517 | 0.0100 |
| Pitch diameter | 0.5405 | 0.5354 | 0.0051 |
Limits of size from ASME B1.1 Table 2.
9/16-24 UNEF tap drill size
Tap drill for 9/16-24 UNEF: 33/64" (0.5156 in, 13.10 mm)
This leaves about 87% thread in the tapped hole.
33/64" is the drill listed for 9/16-24 UNEF in standard tap drill charts. It is 0.0469 in under the 0.5625 in major diameter.
The 2B minor diameter of the finished nut thread must lie between 0.517 and 0.527 in. The charted drill is slightly under that band: the tap trims the crests to size, at the cost of higher tapping torque. A drill inside the band is the safer choice in tough materials.
Other drills that work for 9/16-24 UNEF
A larger drill cuts less thread and taps more easily; a smaller one gives a fuller thread but loads the tap harder.
| Drill | mm | in | % thread | Within 2B limits | Thread engagement |
|---|---|---|---|---|---|
| 33/64"recommended | 13.10 | 0.5156 | 87% | no | |
| 13.1 mm | 13.10 | 0.5157 | 86% | no | |
| 17/32" | 13.49 | 0.5312 | 58% | no |
% thread = (major diameter − drill diameter) ÷ (1.299 × pitch). See the tap drill chart for how to choose a percentage.
Clearance hole for 9/16 in
ASME B18.2.8 does not list the 9/16 in size, so there is no standard clearance hole for the 9/16 in size. Size the hole from the fit the joint needs.
9/16-24 UNEF proof and breaking loads
Loads for steel bolts by SAE grade, from the tensile stress area of 0.214 in². The proof load is the highest load the bolt must carry without permanent set.
| SAE grade | Proof stress (psi) | Min tensile strength (psi) | Proof load (lbf) | Min breaking load (lbf) | Proof load (kN) |
|---|---|---|---|---|---|
| Grade 2 | 55,000 | 74,000 | 11,800 | 15,800 | 52.4 |
| Grade 5 | 85,000 | 120,000 | 18,200 | 25,700 | 80.9 |
| Grade 8 | 120,000 | 150,000 | 25,700 | 32,100 | 114 |
Strengths from SAE J429 for this diameter; stress area from ASME B1.1. Loads rounded to three significant figures.
9/16 in pitches compared
All standard pitches on the 9/16 in diameter. A finer pitch gives a shallower thread, a larger core and a smaller lead angle; a coarser pitch is faster to assemble and more tolerant of damage and plating.
| Thread | TPI | Pitch Ø (in) | Minor Ø D1 (in) | Stress area (in²) | Tap drill |
|---|---|---|---|---|---|
| 9/16-12 UNC | 12 | 0.5084 | 0.4723 | 0.182 | 31/64" |
| 9/16-18 UNF | 18 | 0.5264 | 0.5024 | 0.203 | 33/64" |
| 9/16-24 UNEF | 24 | 0.5354 | 0.5174 | 0.214 | 33/64" |
Closest metric thread
No metric thread is interchangeable with 9/16-24 UNEF. The nearest is M14×1, which is 0.29 mm smaller in diameter with a pitch of 1.000 mm against 1.058 mm. A nut may start on the wrong thread and then bind or strip, so identify by both diameter and pitch.
How the 9/16-24 UNEF dimensions are calculated
Every basic dimension follows from the major diameter and the pitch:
- P = 0.04167 in = 1 ÷ 24 threads per inch
- H = 0.866025 × P = 0.0361 in
- d2 = d − 0.649519 × P = 0.5625 − 0.0271 = 0.5354 in
- D1 = d − 1.082532 × P = 0.5625 − 0.0451 = 0.5174 in
- d3 = d − 1.190785 × P = 0.5625 − 0.0496 = 0.5129 in (external root, 11H/16 deep)
- As = 0.7854 × (d − 0.9743 × P)² = 0.7854 × 0.5219² = 0.21393 in²
- Lead angle = arctan(P ÷ (π × d2)) = 1.42°
Related sizes and tools
Sources: ASME B1.1 (profile, series, limits of size and stress area), ASME B18.2.8 (clearance holes), SAE J429 (mechanical properties) and the tap drill tables of Machinery’s Handbook. How this site checks its data. Last reviewed 29 September 2026.