#1-64 UNC Thread Dimensions and Tap Drill
#1-64 UNC is the Unified coarse thread for the number 1 size (major diameter 0.073 in, 1.85 mm): 64 threads per inch, a pitch of 0.01562 in (0.397 mm), on a 60° profile. ASME B1.1 lists it in the UNC series as a secondary size. Finer threads on the same diameter are #1-72 UNF.
- Tap drill#5367% thread, 1.51 mm
- Pitch64 TPI0.397 mm
- Major diameter0.0730 in1.854 mm
- Pitch diameter0.0629 in1.596 mm
- Minor diameter (nut)0.0561 in1.425 mm
- Tensile stress area0.00263 in²1.70 mm²
- Clearance hole#43normal fit, ASME B18.2.8
Thread profile
#1-64 UNC basic dimensions
| Dimension | in | mm |
|---|---|---|
| Major diameter d = D | 0.0730 | 1.854 |
| Pitch P | 0.01562 | 0.397 |
| Pitch diameter d2 = D2 | 0.0629 | 1.596 |
| Minor diameter, internal thread D1 | 0.0561 | 1.425 |
| Minor diameter, external UNR thread d3 | 0.0544 | 1.382 |
| Height of fundamental triangle H | 0.0135 | 0.344 |
| Thread height, internal (5H/8) | 0.0085 | 0.215 |
| Thread height, external (11H/16) | 0.0093 | 0.236 |
| Crest flat of external thread (P/8) | 0.0020 | 0.050 |
| Crest flat of internal thread (P/4) | 0.0039 | 0.099 |
| Property | Value |
|---|---|
| Threads per inch | 64 |
| Flank angle | 60° (30° each side) |
| Lead angle at the pitch diameter | 4.52° |
| Tensile stress area As | 0.00263 in² (1.70 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.
#1-64 UNC 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 0.0006 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 | 0.0724 | 0.0686 | 0.0038 |
| Pitch diameter | 0.0623 | 0.0603 | 0.0020 |
| Internal thread 2B | Max (in) | Min (in) | Tolerance (in) |
|---|---|---|---|
| Minor diameter | 0.0622 | 0.0561 | 0.0061 |
| Pitch diameter | 0.0655 | 0.0629 | 0.0026 |
Limits of size from ASME B1.1 Table 2.
#1-64 UNC tap drill size
Tap drill for #1-64 UNC: #53 (0.0595 in, 1.51 mm)
This leaves about 67% thread in the tapped hole.
#53 is the drill listed for #1-64 UNC in standard tap drill charts. It is 0.0135 in under the 0.0730 in major diameter.
The 2B minor diameter of the finished nut thread must lie between 0.056 and 0.062 in. The recommended drill falls inside that band.
Other drills that work for #1-64 UNC
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 |
|---|---|---|---|---|---|
| #54 | 1.40 | 0.0550 | 89% | no | |
| 1.5 mm | 1.50 | 0.0591 | 69% | yes | |
| #53recommended | 1.51 | 0.0595 | 67% | yes | |
| 1/16" | 1.59 | 0.0625 | 52% | no |
% thread = (major diameter − drill diameter) ÷ (1.299 × pitch). See the tap drill chart for how to choose a percentage.
Clearance hole for #1
The clearance hole depends only on the 0.0730 in diameter, not on the thread series. The normal fit, a #43 drill, is the usual choice for general assembly.
| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Clearance on Ø (in) |
|---|---|---|---|---|
| Close | #46 | 0.0810 | 2.06 | 0.0080 |
| Normal | #43 | 0.0890 | 2.26 | 0.0160 |
| Loose | #37 | 0.1040 | 2.64 | 0.0310 |
Nominal drill sizes from ASME B18.2.8.
#1-64 UNC strength
SAE J429 starts at 1/4 in, so the SAE grades give no proof load for #1-64 UNC. For an estimate, multiply the tensile stress area of 0.00263 in² by the strength of the material: for example, 60,000 psi gives 158 lbf.
#1 pitches compared
All standard pitches on the #1 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 |
|---|---|---|---|---|---|
| #1-64 UNC | 64 | 0.0629 | 0.0561 | 0.00263 | #53 |
| #1-72 UNF | 72 | 0.0640 | 0.0580 | 0.00278 | #53 |
Closest metric thread
No metric thread is interchangeable with #1-64 UNC. The nearest is M1.8×0.35, which is 0.05 mm smaller in diameter with a pitch of 0.350 mm against 0.397 mm. A nut may start on the wrong thread and then bind or strip, so identify by both diameter and pitch.
| Thread | Major Ø (mm) | Pitch (mm) | TPI | Ø difference (mm) |
|---|---|---|---|---|
| #1-64 UNC (this thread) | 1.854 | 0.397 | 64.00 | — |
| M1.8×0.35 | 1.800 | 0.350 | 72.57 | -0.054 |
How the #1-64 UNC dimensions are calculated
Every basic dimension follows from the major diameter and the pitch:
- P = 0.01562 in = 1 ÷ 64 threads per inch
- H = 0.866025 × P = 0.0135 in
- d2 = d − 0.649519 × P = 0.0730 − 0.0101 = 0.0629 in
- D1 = d − 1.082532 × P = 0.0730 − 0.0169 = 0.0561 in
- d3 = d − 1.190785 × P = 0.0730 − 0.0186 = 0.0544 in (external root, 11H/16 deep)
- As = 0.7854 × (d − 0.9743 × P)² = 0.7854 × 0.0578² = 0.00262 in²
- Lead angle = arctan(P ÷ (π × d2)) = 4.52°
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.