#8-32 UNC thread pitch and dimensions

The #8-32 UNC thread has 32 threads per inch, a pitch of 0.0313 in (0.79 mm), on a 0.164 in major diameter (ASME B1.1). Its basic pitch diameter is 0.1437 in and its basic minor diameter is 0.1302 in.

Threads per inch (UNC)

32 TPI

pitch 0.0313 in · 0.79 mm

Major diameter (D)

0.164 in (4.17 mm)

Pitch (1 / TPI)

0.0313 in (0.79 mm)

Basic pitch diameter (E)

0.1437 in (3.65 mm)

Basic minor diameter (internal)

0.1302 in (3.31 mm)

Tensile stress area (As)

0.0140 in² (9.0 mm²)

Tap drill (75% chart)

#29 (0.1360 in)

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#8-32 UNC basic dimensions (ASME B1.1)
Dimension	Formula	inch	mm
Major diameter D	nominal	0.1640	4.17
Pitch P	1 / TPI	0.0313	0.79
Pitch diameter E	D − 0.649519 / n	0.1437	3.65
Minor diameter (internal)	D − 1.082532 / n	0.1302	3.31
Thread height (basic)	0.541266 / n	0.0169	0.43
Tensile stress area As	0.7854 (D − 0.9743 / n)²	0.0140 in²	9.0 mm²

#8 threads: UNC vs UNF
Thread	TPI	Pitch Ø E	Stress area As	Tap drill
#8-32 UNC (this page)	32	0.1437 in	0.0140 in²	#29
#8-36 UNF	36	0.1460 in	0.0147 in²	#29

Neighbouring UNC threads
Thread	TPI	Pitch (mm)	Minor Ø	Stress area As
#4-40 UNC	40	0.64	0.0849 in	0.0060 in²
#6-32 UNC	32	0.79	0.1042 in	0.0091 in²
#8-32 UNC (this page)	32	0.79	0.1302 in	0.0140 in²
#10-24 UNC	24	1.06	0.1449 in	0.0175 in²
1/4-20 UNC	20	1.27	0.1959 in	0.0318 in²

Practical notes

Unified threads are named diameter–TPI–series: #8-32 UNC is a #8 nominal diameter (number 8 screw, 0.164 in) with 32 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.

32 TPI is a pitch of 0.79 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 #8-32 UNC it is 0.0140 in².

FAQ

How many threads per inch is #8-32 UNC?

32 TPI, a pitch of 0.0313 in (0.79 mm), in the Unified coarse series (ASME B1.1).

What is the minor diameter of #8-32 UNC?

The basic minor diameter of the internal thread is D − 1.082532/n = 0.1302 in (3.31 mm).

What is the tensile stress area of #8-32 UNC?

As = 0.7854 × (D − 0.9743/n)² = 0.0140 in² (9.0 mm²).

What tap drill does #8-32 UNC need?

The standard chart drill is #29, 0.1360 in (3.45 mm), about 69% thread.

What is the difference between #8-32 UNC and #8-36 UNF?

Same #8 diameter, different pitch: 32 TPI versus 36 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)

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