When buying a slot cutter, you have 2 choices to make.
1) Kerf size (1/16" for your needs)
2) arbor size (usually 1/4" or 1/2", some manufacturers offer 3/8" as well).
You need 3 parts for a complete assy.
1) the slot cutter - almost always 1-7/8" diameter
2) the bearing - almost always 7/8" diameter, giving you 1/2" depth of cut
3) the arbor - almost always comes with a few washers and a lock-nut on the end.
If you're ordering online, I suggest you get one arbor, one bearing, and 2 or 3 cutters. There isn't a lot of braze holding that 1/16" piece of carbide on the end of the cutter and it doesn't take much effort to trash your tiny carbide tips. They aren't that expensive and you don't want to pay for shipping one little cutter if you wreck your first one before you complete your project.