For Imperial sized screws and bolts it is the number of threads per inch.
The metric descriptions for threads is a bit less obvious. The distance in
millimeters is used. The problem seems to me to be that the Europeans use
different thread counts than the Asians. This gives a possible three thread
pitches for one diameter. That is where the availability problem arises.
Suppliers keep only what they perceive will be in demand in stock, thus the
manufacturers do not produce quantities here in the Americas.

Dale Davies


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