Quality replacement cylinder sleeves give old cylinders new life. CS – Original barrel has a cast-in iron liner in the cylinder; liner must be bored out completely (do not try to push out the cast-in liner). RS – Original barrel has a replacement sleeve. AC – Original cylinder bore is alloy-chrome plated, nikasil, or electrofused; cylinder must be bored to accept new sleeve. CL – The cylinder’s original cast-in liner will be bored, but not completely removed; sleeve is designed to insert into the iron-lined cylinder.