Allen Head Bolts. The climbing industry standards for bolts in North America is the 3/8-16 bolt.
All the bolts have a thickness of 3/8. The Flat Head is the first bolt, and it is used for the 25 Assorted Smalls. The rest are Socket Head varying in length. All holds paid for on the website include bolts. If you are calling your order in, we will let you know which size of bolt is needed to which holds.