Got it, Robert
I just happen to have a BF618 and it looks like it matches up to the 1-1/2" PVC coupling that's one of my donut dollies. It leaves about 1/16-1/8" around the perimeter of the hammer head. Or should I be going with a smaller PVC coupling? I can try each to see what works best.
I'm not familiar with a shrinking tip on a dent puller. Can you elaborate on that? I may have to go buy another tool.

[on edit] figured it out.

Thanks for your help.
Story time. A few years back, an older man (what am I saying here?

) who had quit driving had his car parked across the street, and I caught some neighbor kids jumping up and down in the roof.

When I told them it wasn't any way to treat the car, they said the old man told them it was OK. I'm not sure I believed them, but they quit. I'd sure hate to try fixing that roof.