1/2-13 UNC thread pitch and dimensions
The 1/2-13 UNC thread has 13 threads per inch, a pitch of 0.0769 in (1.95 mm), on a 0.500 in major diameter (ASME B1.1). Its basic pitch diameter is 0.4500 in and its basic minor diameter is 0.4167 in.
Need it made?
Need a part with 1/2-13 UNC threads machined? Post it free — local makers quote.
Got the machine? Sell your time on The Spool List. Join as a maker
| Dimension | Formula | inch | mm |
|---|---|---|---|
| Major diameter D | nominal | 0.5000 | 12.7 |
| Pitch P | 1 / TPI | 0.0769 | 1.95 |
| Pitch diameter E | D − 0.649519 / n | 0.4500 | 11.43 |
| Minor diameter (internal) | D − 1.082532 / n | 0.4167 | 10.58 |
| Thread height (basic) | 0.541266 / n | 0.0416 | 1.06 |
| Tensile stress area As | 0.7854 (D − 0.9743 / n)² | 0.1419 in² | 91.5 mm² |
| Thread | TPI | Pitch Ø E | Stress area As | Tap drill |
|---|---|---|---|---|
| 1/2-13 UNC (this page) | 13 | 0.4500 in | 0.1419 in² | 27/64" |
| 1/2-20 UNF | 20 | 0.4675 in | 0.1600 in² | 29/64" |
| Thread | TPI | Pitch (mm) | Minor Ø | Stress area As |
|---|---|---|---|---|
| 3/8-16 UNC | 16 | 1.59 | 0.3073 in | 0.0775 in² |
| 7/16-14 UNC | 14 | 1.81 | 0.3602 in | 0.1063 in² |
| 1/2-13 UNC (this page) | 13 | 1.95 | 0.4167 in | 0.1419 in² |
| 5/8-11 UNC | 11 | 2.31 | 0.5266 in | 0.2260 in² |
| 3/4-10 UNC | 10 | 2.54 | 0.6417 in | 0.3345 in² |
Practical notes
Unified threads are named diameter–TPI–series: 1/2-13 UNC is a 1/2 nominal diameter with 13 threads per inch in the coarse series.
These are basic (zero-tolerance) dimensions. Most screws are made to class 2A and nuts to 2B (ASME B1.1), so measured sizes sit slightly below the basic values on the screw.
13 TPI is a pitch of 1.95 mm, which does not match a metric ISO pitch exactly; metric and Unified fasteners of similar size are not interchangeable.
Tensile stress area As is the area used for bolt strength (proof load = As × proof stress for the SAE J429 or ASTM grade). For 1/2-13 UNC it is 0.1419 in².
FAQ
How many threads per inch is 1/2-13 UNC?
13 TPI, a pitch of 0.0769 in (1.95 mm), in the Unified coarse series (ASME B1.1).
What is the minor diameter of 1/2-13 UNC?
The basic minor diameter of the internal thread is D − 1.082532/n = 0.4167 in (10.58 mm).
What is the tensile stress area of 1/2-13 UNC?
As = 0.7854 × (D − 0.9743/n)² = 0.1419 in² (91.5 mm²).
What tap drill does 1/2-13 UNC need?
The standard chart drill is 27/64", 0.4219 in (10.72 mm), about 78% thread.
What is the difference between 1/2-13 UNC and 1/2-20 UNF?
Same 1/2 diameter, different pitch: 13 TPI versus 20 TPI. They are not interchangeable.
Sources: ASME B1.1 — Unified inch screw threads (UN and UNR thread form): basic dimensions, tensile stress area · ASME B18.2.1 — square, hex, heavy hex and askew head bolts and hex, heavy hex, hex flange screws (width across flats)
Find a maker
Post the job free — verified makers quote you.
Post a CNC machining job Open the Thread Pitch & Dimensions Chart calculator