#2-56 UNC Thread
Direct Answer
2-56 UNC is a numbered miniature Unified Coarse machine screw thread with a major diameter of 0.0860 inches (2.184 mm) and 56 threads per inch (TPI). Requiring a #50 (0.0700 inch) tap drill, it is widely used in precision model engineering, musical instrument pickups, and micro-electromechanical assemblies.
Source: ANSI/ASME B1.1 (Unified Inch Screw Threads)
Specs
| Nominal Major Diameter | 0.0860 in (2.184 mm) |
| Threads Per Inch (TPI) | 56 TPI (Coarse pitch: 0.454 mm) |
| Fine Pitch Equivalent | #2-64 UNF (0.397 mm pitch) |
| Tap Drill Size | #50 drill bit (0.0700 in / 1.78 mm) |
| Minor Diameter (Internal) | 0.0667 in (1.694 mm) |
| Tensile Stress Area | 0.00370 in² (2.39 mm²) |
| Thread Profile Angle | 60 degrees |
Miniature Instrumentation and Guitar Hardware
2-56 screws are the classic standard for electric guitar single-coil and humbucker pickup height adjustment screws (Fender/Gibson) and small electromechanical relay mountings in aerospace instrumentation.
Tapping and Machining Considerations
Because the minor diameter is under 1.7 mm, #2-56 taps are fragile. In aluminum and brass, tapping fluid and frequent chip clearing are required to prevent tool bind.