1/4"-20 UNC vs. 3/8"-16 UNC
Comparing 2 standards across 7 specifications. 7 key differences identified.
1/4"-20 UNC is a fractional Unified Coarse machine screw thread with a major diameter of 0.2500 inches (6.350 mm) and 20 threads per inch (TPI). Requiring a #7 (0.2010 inch) tap drill, it is the universal global standard under ISO 1222 for camera tripod mounting sockets, studio light stands, and general machinery bolting.
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.
Specification Comparison Table
7 Parameters| Parameter / Spec | ||
|---|---|---|
|
Nominal Major Diameter
|
0.2500 in (6.350 mm) | 0.3750 in (9.525 mm) |
|
Threads Per Inch (TPI)
|
20 TPI (Coarse pitch: 1.270 mm) | 16 TPI (Coarse pitch: 1.588 mm) |
|
Fine Pitch Equivalent
|
1/4"-28 UNF (0.907 mm pitch) | 3/8"-24 UNF (1.058 mm pitch) |
|
Recommended Tap Drill Size
|
#7 drill bit (0.2010 in / 5.10 mm) or 13/64 in | 5/16 in drill bit (0.3125 in / 7.94 mm) |
|
Minor Diameter (Internal)
|
0.1959 in (4.976 mm) | 0.3073 in (7.805 mm) |
|
Tensile Stress Area
|
0.0318 in² (20.5 mm²) | 0.0775 in² (50.0 mm²) |
|
Common Drive Size
|
7/16" Hex (11.11 mm) / 3/16" Allen (4.76 mm) | 9/16" Hex (14.28 mm) / 5/16" Allen |