As I have just found a 29mm seal in my spares that I had assumed was a diana 28mm seal (same parachute, ploy type seal with a female centre tovetail fitting, like a TX). But at a full 29mm (maybe 29.2), it's never going to go into a 28mm tube...
It might actaully go well in my britinia, which is about 28.5 - with a little resizing, but curious what it's for ?
Rgds - JB