3/8"-16 UNC
Imperial Threads (UNC/UNF) · 7 specs
Direct Answer
3/8"-16 UNC is a fractional Unified Coarse machine screw thread with a major diameter of 0.3750 inches (9.525 mm) and 16 threads per inch (TPI). Requiring a 5/16 inch (0.3125 inch) tap drill, it is the international standard for professional photography tripod-to-head mounting studs, cinema camera baseplates, and stage microphone stands.
Source: ANSI/ASME B1.1 / ISO 1222 · Last reviewed Aug 28, 2026
Specs
| Nominal Major Diameter | 0.3750 in (9.525 mm) |
| Threads Per Inch (TPI) | 16 TPI (Coarse pitch: 1.588 mm) |
| Fine Pitch Equivalent | 3/8"-24 UNF (1.058 mm pitch) |
| Recommended Tap Drill Size | 5/16 in drill bit (0.3125 in / 7.94 mm) |
| Minor Diameter (Internal) | 0.3073 in (7.805 mm) |
| Tensile Stress Area | 0.0775 in² (50.0 mm²) |
| Common Drive Size | 9/16" Hex (14.28 mm) / 5/16" Allen |
Heavy Photographic and Audio Mounts
While cameras attach to quick-release plates using 1/4"-20 screws, the ball head or fluid head attaches to the tripod legs using a heavy-duty 3/8"-16 UNC center bolt. In European studio audio, European microphone clips use 3/8"-16 threads (adapted to US 5/8"-27 threads via brass adapter rings).
Automotive and Industrial Framing
Widely used in automotive suspension brackets, alternator tensioners, and structural steel clamps where high clamping force is required.