Odd powder drum threads

[SandWatcher]

I'm replacing a corroded powder drum on a .45 rifle barrel, manufactured for a kit in the 1960s or 70s. The only markings are "Spain" and a six digit serial number. I have a some new drums from ToW of various sizes (including a CVA drum), but nothing matches what came out of this barrel. I've measured the original several times, and it looks like it needs 3/8-20 threads. Has anyone heard of such a thing? Am I going to need to fabricate a replacement from scratch?

 

[Colonial Boy]

As it’s a Spanish gun the threads will, almost certainly be Metric.
3/8 , 20 is a BSF size

 

[smokeum54]

Been awhile but the last spain/cva i had out was 10x1.25 if i remember correctly.