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



Hi Dale,

The Europeans and the Asians use the same which is metric threads. You
either have threads per inch (Imperial thread system)  or you have the
distance between threads in mm (Metric thread system).

What would be the third thread pitch definition that you seems to know
about?

In Imperial a higher thread count is a finer thread, and in Metric a higher
thread number represents a coarser thread.

Regards
Rolf



I found years ago when we first got introduced to import vehicles, that most bolt
suppliers in North America had not started to manufacture metric bolts and screws. At that
time the only source was the dealers or wreckers. When going to dealers, a bolt for a
Japanese car MAY not be found at or fit a European thread. Take the 10mm size. You may
have 1.0 and 1.5 in European and 1.0 and 1.25 from Japan. No third standard, just an extra
pitch from a different country or area. Honda and Toyota used odd size bolt heads;11,13,
15, 17, and 19mm. Mazda used 8, 10, 12, 14, 17, 19mm wrench sizes. They had different
suppliers or engineering spec'd  different head sizes. Two bolts could be 8mm with
different heads. Kind of the same idea as the differing thread pitch. The thread pitch
difference seemed to be European preference as to Japanese preference in some sizes.

Dale Davies