How to attach a timing wheel to a crank?

After a bit of research, I think I now know what you are talking about. You left out a lot of detail on this post; next time, some links would come in handy. For anyone else reading this post, here's a link tithe Comp Cams web site:

COMP Cams Catalog - Sportsman Professional Degree Wheels Crankshaft Sockets

RJ is talking about the Crankshaft socket at the bottom. This locates the degree wheel on the crankshaft rather than the cam, and provides a way of turning the crank without removing the wheel.

I've never rebuilt an engine nor timed it that way, so I couldn't tell you the benefits. At a guess, I would say the crank degree wheel might offer a bit more precision due to its size, but that's all I can see.