Yeah Beaner the Rm is a single ring, along with yz, and cr,s that I owned from 87 to 06, I,m sure the kx is a single ring too. The skirt- bottom of the piston has a full length-same length skirt. A top engine builder will tell ya to run a gp piston. The gp piston is heavier than a stock or pro lite piston, just so ya know. Alot more durable tho, just get the gp piston designed for your RM, I don,t think you want to run a diff. rod just to change the piston and run the bill up to 2,400 plus.