[Leica] Making a back to back lens coupler

[Dennis Painter <dpainter@bigfoot.com>]

I want to glue two of the latest rear lens caps together to make a back
to back lens coupler. The grey thing leica sells should be closed and
deeper for 21mm lens, etc.

I figure if I just glue them tother they will separate, at a most
inopportune time. Anyone do this and know what works?

It does look like that ridge should be sanded down to improve the
contact surface area.

TIA,
Dennis