#2-56 UNC thread

#2-56 UNC is a coarse Unified inch thread with a 2.184 mm (0.086") major diameter and 56 threads per inch (0.454 mm pitch). Tap it with a #50 drill; drill 2.44 mm to pass a bolt through.

The numbers

Designation

#2-56 UNC

Major diameter

2.184 mm / 0.086"

Minor diameter

1.693 mm

Pitch

56 threads per inch (0.454 mm pitch)

Tap drill (75% thread)

#50 — 1.78 mm

Clearance hole (close fit)

2.44 mm / 0.096"

How to measure what you have

1. Measure across the thread crests with calipers. A used #2-56 UNC reads a little under 2.184 mm — the crests are truncated by the standard, then worn and plated, so anything from about 1.8 mm up is consistent with this size.
2. Count the threads crossing one inch. This one gives 56.
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

No torque figure is given for this size. Small and fine threads like this are generally not supplied to a strength grade, and in most assemblies the tapped material strips before the fastener yields — so a published bolt torque would be the wrong limit to work to. Tighten to snug plus a small turn, or use the figure the manufacturer of the part specifies.

Where this size turns up

• Model railway track and rolling stock fittings
• Terminal strips and small electrical hardware
• R/C servo horn and linkage screws

Other threads at this diameter