how to I.D. for proper flywheel puller?

hey everyone...
have everything going on my 73 CR250 except I sheared my crank key.
there is a local guy way up here in Northern B.C., Canada,
that has a puller, but you can't get ahold of him easily, and he won't part with it. He will pull your flywheel if you load up and bring it to his shop miles and miles away.
I need a puller.
I see them all over for sale on the net, but am going crazy trying to research the proper thread size/pitch etc. so I can get it right the first time! Please help.

Thanks for that tip John!
Will folllow up.