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




  Hi  Paul,
                   After about 50 years since first intro to metric
bolts, VW and Peugeot cars, I found that the Germans and French used a
bigger nut size and bolt head size like 17 mm and 19 mm  for 10 mm
bolts, 13 mm for 8 mm bolts and 11 mm for 6mm bolts, on VW they started
using 10 mm bolt head and nuts on 6 mm bolts, then they started smaller
bolt head and nut sizes, but I think still use 13 mm for 8 mm bolts Japs
use 12 mm head bolts and nuts, and on 10 mm bolts Japs use 14 mm head
bolts and nuts. Both regions use 1 mm pitch for normal 6 mm bolts but
Europe seem to use one step coarser thread pitch on bolts e.g..,
Japs may use 1.25 pitch on a bolt threaded into steel, Europe will use
1.5 mm pitch in same application, Japs seem to use a finer pitch bolt
when tapped into
alloy whereas US and Europe will use a coarser pitch.
                John Burey