Nylon pulley with screw - this is a lightweight pulley that is galvanized. Sizes 3652S-06,08,09,10,12 = white nylon pulley. Please note that the sizes listed in the "Specific Technical Information" for the value "f" differ for these codes. Currently - 3652S-09: f=7.5mm; 3652S-12: f=7.5mm.