TPI stands for threads per inch, the number that follows the diameter in an inch thread callout, as in 3/8-16. Pitch is its reciprocal, so 16 TPI is a pitch of 0.0625 in. A screw pitch gauge or a steel rule laid along the crests reads it quickly, and on metric hardware the idea is replaced by pitch stated directly in millimeters.
It's three-eighths, but I can't tell if it's 16 or 24 TPI, put the pitch gauge on it before you force a nut.
Also heard as
- threads per inch
Related terms
Pitch
The distance from one thread crest to the next, measured parallel to the screw axis.
UNC
Unified National Coarse: the standard coarse inch thread series, such as 1/4-20, 3/8-16 and 1/2-13.
UNF
Unified National Fine: the inch thread series with more threads per inch, such as 1/4-28, 3/8-24 and 1/2-20.
Lead
The distance a thread advances along its axis in one full turn, equal to pitch times the number of starts.