BDZMC Piston Ring Compressor Tool, Adjustable Sizes from 2.09" to 6.9 DB TAC Skeletonized 223 5.56 308 Buttstock for 6 Position Mil Spec 5394654 Cummins X12 Piston Ring Compressor Tool Piston Ring Compressor For Small Engines at Ryder Sturdee blog. Putting the connecting rod through first, simply place the piston, with rings, into the tapered end of the ring compressor. Tighten the compressor snugly around the base of the piston. Then lay the compressor flat on the engine cylinder bore. Sold individually. Product Details: Adjustable Piston Ring Compressor Tool Unit has a 4. 000 Inch to 4. 090 Inch Bore Range Blue Anodized Finish Made from High Quality Aluminum Material Sold As Each