Specially ground, reduced-diameter pilots fit the tighter bore specifications used on all Nowlin barrels. Will also provide a satisfactory fit in most other brands of barrels. Each smooth-cutting, six-flute reamer is precision ground with an integral throater and solid, fixed pilot. Mfg: Manson Precision SPECS: M7 high speed steel. Six straight flutes with right hand cut. 3/8" (6.3mm) square drive shank.