Imperial Fine (UNF) Bolts — Complete Size Reference
Complete reference for imperial UNF (fine) bolts from 1/4-28 to 3/4-16. Wrench sizes, torque specifications, and applications.
1/4-28 UNF7/16 wrench · 28 TPI · 12 Nm5/16-24 UNF1/2 wrench · 24 TPI · 22 Nm3/8-24 UNF9/16 wrench · 24 TPI · 47 Nm7/16-20 UNF5/8 wrench · 20 TPI · 70 Nm1/2-20 UNF3/4 wrench · 20 TPI · 110 Nm9/16-18 UNF13/16 wrench · 18 TPI · 150 Nm5/8-18 UNF15/16 wrench · 18 TPI · 210 Nm3/4-16 UNF1-1/8 wrench · 16 TPI · 350 Nm
About UNF bolts
UNF (Unified National Fine) bolts have more threads per inch than UNC (coarse) bolts of the same diameter.
Advantages of UNF threads
- Better vibration resistance
- Finer adjustment
- Higher tensile strength
- Common in automotive and aerospace
UNF vs UNC
For example, 3/8-24 UNF has 24 threads per inch, while 3/8-16 UNC has only 16 threads per inch. The fine thread provides better performance in high-vibration applications.