T6 Aluminum (Tempered Aluminum): T6 Aluminum is light weight, has a high strength to weight ratio, durable, and resistant to corrosion.
Brass: Brass, besides being extremely durable and corrosion resistant, offers low friction where two brass surfaces come into contact (e.g. tuning slides).
Acetal Copolymer (Delrin®): Acetal Copolymer is a very dense and durable plastic that is FDA approved.