Threads per inch, or TPI, and thread pitch are different but related methods of measuring the position of the threads on a screw, bolt, or fastener. The thread is the helical protrusion that is found along the length of these parts. TPI is a numerical representation of the number of threads in every inch of length along a screw. The thread pitch is a measurement of the distance between two thread peaks. Thread pitch is used when measuring or referring to metric parts. Both the TPI and thread pitch of a screw, bolt, or fastener can be converted between the alternative value using conversion tables, calculators, or a mathematical formula. Knowing the TPI or thread pitch of a particular part is important information for knowing whether the part will fit into the space it is supposed to go.
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