UNI-SPOTTER WELDING STUDS Uni-Stud 2.2mm & 2.6mm Pulling Pins Premium Performance Dimple HeadThe 1001 Flexpert Welding Studs are the most popular stud sold. They are 2.2 mm, copper coated and have been specially designed for easy welding and easy removal after the pulling is complete. The shafts are strong yet flexible. This is the preferred stud for use with slide hammers.