synchronous belt pulley (XL,L,H,XH,XXH) HTP Timing ... Timing pulleys (T2.5,T5,T10,T20,AT5,AT10),et synchronous belt pulley (XL,L,H,XH,XXH) HTP Timing pulleys ... T20,AT5,AT10),BTL Timing pulleys(L,H,XH)The surface treatment of timing belt pulleys is black phophated(except ... .material: 45C,GG25,FFF40,Aluminium,nylon,stailess steel,etc.surface treatment:black oxide,phosphate,anodize and zinc plating.