 These were used in two ways, either with pickup and buffer module mountable to the guitar, or as a "GK-KIT" intended to be fitted into a guitar body by a luthier or manufacturer.The initial GK-1 had 24 output pins, with a resultantly bulky interface cable.The design evolved into a smaller 13-pin format, used in the GK-2, GK-2A, and GK-3 pickups, as well as the GK-3B bass pickup.