Only a few kits, sold by Berea Hardwoods and their resellers, use the B mandrel. I have not seen any other company's kits use the B mandrel...although I could be wrong....I have been before...more than once.
Woodcraft sells Berea kits and all of them use the A mandrel...even if Berea suggests the B mandrel. Woodcraft has the bushings for the A mandrel for all of their kits. If I purchase a kit that requires the B mandrel I get bushings from Woodcraft for that kit. It is a little confusing because Woodcraft changes the names of some of their kits from the name used by Berea. You will soon learn how all of this works.
Do a good turn daily!
Don