Generally speaking, the model engineering suppliers are very much cheaper than
RS or Farnell, and in many cases, just as fast. Some of them can even supply
'off the shelf, next day delivery' such niceties as a 3/8-32tpi UNEF tap or die
(UG1094 BNC socket thread) or 5/8-32tpi UNEF, which is type N or UHF socket
thread. I can't remember what an SMA thread is, but there's a good chance one
of the suppliers will have it in stock.
Tufnol is used in model engineering for making (from thin sheet material) leaf
springs for locomotives and other rolling stock axleboxes. PTFE (Teflon) rod
and sheet is used for clack valve seatings by some people, so these materials
are available. In this respect the UK is much better off than most other
countries, having a lot more suppliers. The model engineering suppliers are
becoming the last sources of BA fasteners, too. Unified threads seem very hard
to get except from specialist suppliers in UK. Interestingly, the Unified
screws, having a coarser thread, are far better in soft materials like tufnol
(and aluminium) than the ISO metric stuff. On this tack, does anyone know why
the US seemed to have moved from using 4-36 threads to 4-40 threads over the
period of about 1946 to 1952?
73
Peter W6/G3RZP
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