Checkered Flag Performance 4.000" tapered piston ring compressors make installing piston rings a simple and easy part of your engine build or rebuild. Install your rings onto your piston, then slide the piston / ring assembly into the tapered bore of the ring compressor until the piston skirt starts to come out the bottom of the tool. Insert the piston skirt into the cylinder bore and allow the tool to sit flat on the cylinder deck. Press the piston assembly through the tool and into the cylinder bore. The tapered, true radius inner diameter of the tool compresses the rings as you push it through. Use assembly lube or engine oil to ease installation. Do not be fooled by the low price, these are high quality, well made tools suitable for the professional technician as well as shade-tree mechanics and hobbyists. You can pay for a big brand name, or you can add this high quality tool to your set at a much lower price. This ring compressor is a bore specific fixed size (4.000 inch) and non-adjustable. This piston ring installation tool has a lifetime warranty. It is recommended to use a piston groove cleaner tool, piston ring gap filer (or grinder), ring squaring tool, piston ring installer tool (or ring expander pliers) and engine assembly lubricant to help ensure that your engine rebuilding project goes smoothly.