material from above 3 kinds of material, copper, brass, alluminum. size: less than 20mm, +/-0.02mm ID and OD, +/-0.05mm length The reason to choose us: 1, matured product, accurate in size, can keep good tolerance.2, low price, we are using automatic machine to cut it.after process such as press the hole, shrinking 1 end available.3, good and fast service.