As a common problem with running the RRS Anvil 30 bowl inside of our tripod is there locking ring does not match up with our locking system. So we set out to make a bowl that fit perfectly. This bowl featuers a locking ring which is compatiable with all our 75mm opening tripods. Manufactured from 6061 aluminum featuring a main stud and the 4 small locking screws to stop your anvil 30 from rotating. Proudly made here in the Good Ole USA.