B&B's Tapered Ring Compressors reduce assembly time and eliminate distortion and breakage of rings during assembly. Each ring compressor is precision machined from heat treated aluminum. The ID dimension is finished hone to proper tolerance. The OD is machined with an exclusive Posi-Grip surface to prevent oily hand mishaps. Each ring compressor is finished with a hard anodization to insure years of service. Truly the professional way to install pistons.