1/2" shank with a 5/8" diameter cutter. If you are not 100% satisfied with these bits, send them back for a refund.
I have been ordering from Rockler for almost 20 years and have found their products to be very inexpensive and of high quality. Shipping is fast even when an item is back ordered. The best prices I have found anywhere."- Orval - 08/07/2012