Just slide the piston and rod assembly down into the tapered ring compressor. The taper will create a squeezing of the piston rings  allowing the piston and rod to gradually enter the engine bore. Slight tapping of top of piston will allow piston to enter bore smoothly. 

Will help simplify the piston installation process during engine building. Most all bore sizes available. Message for your specific bore sizes needed. OVERSIZED BORES ARE NO PROBLEM.