These high speed steel finish reamers are designed exclusively for finish sizing cast iron valve guides. They are piloted for easy centering in the guide bore. The pilot area measures .012" smaller than the finish diameter. With proper care, these reamers will accurately size multiple guides without losing their efficient cutting action. We recommend using these reamers at 400 to 500 RPM for the best finish. For best results use high speed steel finish reamers exclusively on cast iron without reaming oil. Always wear eye protection.