HELLS ANGELS SINGLE BALL PEAN HAMMER PIN - GOLD - THE ULTIMATE IN HAMC SUPPORT PINS -  A ball-peen or ball pein hammer, also known as a machinist's hammer, is a type of peening hammer used in metalworking. Its really good in denting gas tanks and tough guys or the occasional smart ass. It has two heads, one flat and the other, called the peen, rounded.