7/16"-20 UNF thread

7/16"-20 UNF is a fine Unified inch thread with a 11.112 mm (0.437") major diameter and 20 threads per inch (1.270 mm pitch). Tap it with a 25/64" drill; drill 11.91 mm to pass a bolt through.

The numbers

Designation

7/16"-20 UNF

Major diameter

11.112 mm / 0.437"

Minor diameter

9.738 mm

Pitch

20 threads per inch (1.270 mm pitch)

Tap drill (75% thread)

25/64" — 9.92 mm

Clearance hole (close fit)

11.91 mm / 0.469"

Hex across flats

15.88 mm

How to measure what you have

1. Measure across the thread crests with calipers. A used 7/16"-20 UNF reads a little under 11.112 mm — the crests are truncated by the standard, then worn and plated, so anything from about 10.7 mm up is consistent with this size.
2. Count the threads crossing one inch. This one gives 20.
3. A thread pitch gauge settles it in seconds and costs very little. Guessing between a coarse and a fine thread of the same diameter is the usual way a thread gets stripped.

Tightening torque

Plain steel property class 8.8 or SAE grade 5, dry threads, tightened to about 65% of yield. Lubricated threads reach the same preload at 20-30% less torque. Where the manufacturer publishes a figure — spark plugs, wheel nuts, cylinder heads — use theirs.

Where this size turns up

• Connecting rod and spindle nuts in US engines
• Automotive suspension fine-thread studs

Other threads at this diameter