ST-58 thread type is double thread design for easy knock off drill bit, ST-58 means diameter 58 mm with double T shape thread, thread distance 24 mm, this is extra heavy duty drill bit for jump top hammer. Drill rod use guide tube for a match.
18 Dome/Semi-ballistic carbide inserts ST58 Threaded drill bits with flat face design, 89 mm diameter with extension rod for heavy duty drilling.