In article .com,
Mr Uncalled-For writes
On Aug 15, 9:53 am, fred wrote:

Try part no 16148, 82 mm, black, strap boss, 2/3 down this page:http://www.bes.
ltd.uk/products/130a.asp
Boss adaptors here, top of the page:http://www.bes.ltd.uk/products/130b.asp

But a local plumbers' merchant or drainage supplies place should do the
same. It is 3" nominal so that is what you should be asking for.

Thanks. It's exactly 3.5 inches external though - I'm not sure if
that's the same as 3 inches nominal.

The one at BES is 82mm so 3.25" which is plenty close enough for a strap
on boss but buy a longer bolt for the back fixing which I'd guess will be M6.

Last one I fitted needed a 57mm hole saw for the pipe, cut slow and use
lube.
--
fred
Plusnet - I hope you like vanilla