[Amps] Conversion Nightmare

[Peter Chadwick]

Getting back to something to do with amplifier building, to my mind, one of the abominations of the metric system is the ISO metric thread. Even the ISO metric coarse is far too fine a thread for many applications, especially tapping into aluminium, or heavens forbid, that horror to work, copper. UNF and UNC or BSW and BSF are far better in this respect, while for small screws, the US threads are good. Incidentally, does anyone know why the standards apparently changed from something like 4-36 to 4-40 in about 1950 or so? I also do not understand why we had to stop using the BA thread, which is actually a metric thread anyway, developed originally by the Swiss!  And because of the 47-1/2 degree, somewhat stronger than 60 degree threads.
I know you can use coil inserts, but that seems to me to be adding unnecessary complication  for the sake of using something that is not right for the job. Interestingly, the model engineering people are firmly wedded to BA: one advantage is apparently that the odd numbers tend to have heads that are relatively close to scale.
One day, I must get around to getting a die to match  my 5/16 left hand Whitworth tap......


73

Peter GW3RZP/P