Side-by-Side Comparison
Imperial Threads (UNC/UNF)
1/2"-13 UNC vs. 1/4"-20 UNC
Comparing 2 standards across 7 specifications. 7 key differences identified.
Comparing:
1/2"-13 UNC
1/4"-20 UNC
1/2"-13 UNC is a heavy fractional Unified Coarse bolt thread with a major diameter of 0.5000 inches (12.700 mm) and 13 threads per inch (TPI). Requiring a 27/64 inch (0.4219 inch) tap drill, it is the standard structural fastener for automotive engine cradles, trailer hitches, and building timber connections.
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.
Specification Comparison Table
7 Parameters| Parameter / Spec | ||
|---|---|---|
|
Nominal Major Diameter
|
0.5000 in (12.700 mm) | 0.2500 in (6.350 mm) |
|
Threads Per Inch (TPI)
|
13 TPI (Coarse pitch: 1.954 mm) | 20 TPI (Coarse pitch: 1.270 mm) |
|
Fine Pitch Equivalent
|
1/2"-20 UNF (1.270 mm pitch — standard automotive wheel lugs) | 1/4"-28 UNF (0.907 mm pitch) |
|
Recommended Tap Drill Size
|
27/64 in drill bit (0.4219 in / 10.72 mm) | #7 drill bit (0.2010 in / 5.10 mm) or 13/64 in |
|
Minor Diameter (Internal)
|
0.4167 in (10.584 mm) | 0.1959 in (4.976 mm) |
|
Tensile Stress Area
|
0.1419 in² (91.5 mm²) | 0.0318 in² (20.5 mm²) |
|
Common Drive Size
|
3/4" Hex (19.05 mm) / 3/8" Allen | 7/16" Hex (11.11 mm) / 3/16" Allen (4.76 mm) |