This Flat Idler Pulley is for use as a general purpose pulley for power transmission such as compressors, industrial fans, lawnmowers, snowblowers and electrical motors. It comes with a bore adapter to bush down from 17mm to 5/16 inside diameter. 31288150 features a heavy duty sealed radial single-row bearing.This part is Zinc-coated for long-term rust prevention. Additional Features: Made of Steel Flanges angled outward to help increase belt life