The drill crew was on the rig floor changing out the rig tongs from type-DB to type-C. The DB tongs had been removed from the make up tong side and the type C tongs were attached to the tong cable. The type C tongs were being lowered by the air hoist and the weight of the tongs was transferred from the hoist line to the tong line. The tongs stopped at about 2.5 feet from the rig floor where one of the floormen was able to remove the hoist line. Once the hoist line was removed, the shackle pin at the counterweight bucket had come out of the tong cable causing the tong to drop to the rig floor.