BK45-5/8" ID 5/8"Bore cast iron Solid Pulley with 4.25" inch OD for V-belts size 4L, 5L (BK4558)1 Groove BK45 5 8" ID 5 8" ( 0. 625" ) Bore cast iron Solid Pulley with 4. 25" inch OD for V belts size 4L, 5L (BK4558) BK Finished Bore Sheaves for (4L or A or 5L or B Belts)BK Sheaves are accurately machined from fine grained cast iron, statically balanced,They are furbished with Standard Keyseats and Hollow Head SetscrewsThe V Belts you that can run in this pulley are 4L, or A or 5L, B, V Belts. The belt series most common for this pulley is the 4L