In the early 20th century, before welding was widely developed and before high-strength steel bolts were used, metal construction commonly relied on the painstaking process of riveting. For the Shamrock tower, steel plates were fabricated and sometimes preassembled at the Washington Heights shop, with each rivet hole pre-punched during fabrication. Riveting was done both on the ground as each bay was assembled and in the air as the bays were joined together, with a leather-like material placed between each seam before riveting. The process usually required four men: the forge man, the catcher, the rivet man, and the buck man or bucker. A forge heated rivets red hot near a seam, the forge man tossed a rivet to the catcher, who caught it in a catcher can, and the rivet was then removed with tongs and placed in the hole. The rivet man drove it in with an air hammer weighing from 35 to 60 pounds while the bucker held a bucking bar, or rivet set, against the seam and over the unformed end known as the buck tail. Bucking the rivet caused the buck tail to mushroom into a domed shape, and as the rivet cooled it contracted and tightened the joint. This process was repeated approximately 12,000 times during the building of the Shamrock tower.