Aluminum arms 1.25" diameter with flat milled plus 5/16" hole to mount Wheels. Arms and Wheels and bearings for the Clark Steady Rest ordered separately only if ordering after initial purchase. Arms and wheels and bearings come standard and are ordered when building your steady so it is not necessary to order here. This section is only if ordering extra after the initial order. Don't forget to order wheels and bearings if needed which include the attachment hardware. Also indicate on your order the length of the arms needed for your lathe.