Let me make a correction on the above post as the Sauer Patent was noting the means of attaching the tubes: AMERKIA - 505006 - http://www.google.com/patents?id=pf1JAAA...;q=&f=false

The correct Patent numbers are as follows:

BELGIEN - 102613
FRANKREICH - 226603
OESTERREICH - UNG. 21471/69130
DEUTSCHLAND - 70343
ENGLAND - 23496
AMERIKA - 505006

I think Sauer to be the source of the Rigby style forend latch forends, or to have a direct source.

Kind Regards,

Raimey
rse