the 306 atty is pretty much the same as a 401, dippable type, and it has 510 type threads, so it screws right onto the 510 adapter. I originally tried 401's on my prodigy, but it popped them constantly, they usually lasted between 1 hour and a couple days before failing. I swithched to 510's which lasted well, then tried 306's on my 510 adapter. The 306's are holding up quite well on my prodigy, so they seem to be much stronger than 401's, and you dont need a 401 adapter.