The final design for the T-13 hand grenade utilized a pressure trigger as well as an in-flight armingdevice. The grenade was designed to be thrown as a traditional baseball, and as such it was held with two fingers on a weighted and knurled "butterfly cap" and the arming pin was removed. Once thrown, the cap detached from the body of the grenade and a length of nylon string unwound until a secondary arming pin attached to the far end of the cord was pulled, arming the grenade to detonate upon impact with a hard surface. While the original design called for a total weight, it was later decided that this was too light and the weight was increased to.