About ThreadSpec.org — Thread Specification Reference

ThreadSpec.org is a comprehensive thread specification reference designed for engineers, machinists, maintenance technicians, and makers. Our goal is to provide accurate, easy-to-access thread data for the most commonly used thread standards worldwide.

Data Sources

Every dimension on this site is calculated directly from published engineering formulas — not copied from other charts or databases. This ensures consistency and allows us to show exactly how each value is derived.

ISO 724 — Metric thread geometry (pitch diameter, minor diameter, thread depth)
ISO 261 — Metric thread standard pitches
ISO 898-1 — Metric fastener property classes and proof loads
ASME B1.1 — Unified inch thread dimensions (UNC, UNF, UNEF)
ASME B1.20.1 — NPT pipe thread specifications
ISO 228 / BS 21 — BSP pipe thread specifications

Coverage

Our database currently includes 207 thread specifications across six major standards:

36 ISO Metric Coarse sizes (M1 to M68)
56 ISO Metric Fine sizes
33 UNC (Unified National Coarse) sizes
24 UNF (Unified National Fine) sizes
22 UNEF (Unified National Extra Fine) sizes
19 NPT (National Pipe Taper) sizes
17 BSP (British Standard Pipe) sizes

Contact

Questions, corrections, or suggestions? Email us at [email protected].