Clevis mounting holes are for 5/8" bolts. Mounting holes are slotted to permit installation without removing insulators. Material: Hot Dip Galvanized. The J1300 is designed to develop high strength on deadends or line pulls. It has a mounting slot for one 5/8 inch machine bolt and two staggered side holes for 1/2 inch lag screws. (Manufacturer: MacLean Power Systems)