The bolt that attaches the Hulme to the reloader base has a 5/16-24 thread. The length of the bolt depends on the style/vintage of the Hulme case feeder. The most common Hulme uses a 2 1/2" long bolt. The old style uses a 5/8" long bolt. There is an intermediate style that looks like the newer ones, but has a large hole through the side (you sent me a picture of one). I think this one also uses a 5/8" long bolt, but I'm not sure, and don't have one at this moment to check.