I found this odd projectile and cleaned the rust off and blued it.
It looks like a French style band but I think it may have been home-made.
There are casting flaws in the metal. Deep threads to about 6mm above the top band, then it widens out and has a flat bottom. I show it with a French 37mm fuze but it also fits the British 1Pr fuze. 1.5mm metric size. Dimensions are:
107.5mm overall with fuze.
31.3mm top band.
32mm drive band.
What 30mm? case would it fit? Real, fake or miniature? Comments are welcome.