What kind of Wide Five Drum is this?

[cas3]

I think its a bolt on to make either the hub or drum replaceable if need be. Imagine there is probably some NOS drums around that nobody knows what they fit!

This one was really good on drum wear, only .15 or so, but the hub had sat outside for decades and wrecked the bearing surface. Lars had a plan to re-machine the hub to take a different bearing. He has a beautiful old school 34 highboy roadster. He's a member here...perhaps will chime in