... ,XXL,SL9,SL12,SL,HTD:3M,5M,8M,14M,20M AND SO ON2. Metric System: T-type series(T2.5,T5 ... ,H,X6. Material:1045 carbon steel, aluminum alloy frequently used,brass and nylon available.7. Surface treatment:black oxdizing,phosphating,anodize,zinc ...