... efficiency NOVO's timing pulley:1. Plain bore: MXL, XL, L, H; T2.5, T5, T10; AT5, AT10; HTD 3M ... , 5M, 8M, 14M.2. Taper bore: XL, L, H, XH; HTD 5M, 8M,14M.3. Material: Aluminium, Cast ... Iron, Steel.4. Surface Treatment: Black, Phosphate, Zinc Plating, Hard anodized, Nitriding, Dichromate.5. Teeth Number is from ... :We've been ISO9001:2000 certified since 2003. L-H Taper pulleys