MG TC Petrol Cap Assembly?

[Chris Blood]

Out of frustration, could anyone help me to solve a problem I have with my
petrol cap? I have a new cap with gubbings (from Moss) and an old
(presumably original) catch to hold it down. However, how do the two marry
up to each other. I reckon the catch may be the wrong one!
Does anyone have a diagram of the components that show the catch dimensions
and how it works?
cheers in advance if you can help.
Chris Blood (TC 3686) Ex Police Car
Notts, England