See if formatting is better;
Peter,
See below,
On Sun, 23 Jan 2005 09:34:48 -0500, <G3rzp@aol.com> wrote:
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?
My guess is because 4-40 screws have more holding power than a 4-36
screw does. This is due to more threads in the thickness of whatever
it's screwed into, either tapped material or a nut. Fine threads are
always used in places where more holding power is needed in a thin
section. Coarse threads are for thicker sections.
73
Peter W6/G3RZP
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Will
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