I'm currently looking for this part on an Original/Diana diopter...
Rare as rocking horse poo to find, but thought I'd ask on here...
I believe it does have a specific name, "retaining foot" or something along them lines. .
Any help would be appreciated.
Thanks Ian...

https://ibb.co/r4XC1Yc
https://ibb.co/hDVGP01
https://ibb.co/m8Sbwnz