Spring loaded chain tensioner for running Single Speed on non-adjustable chain tension frames. Fit to rear mech hanger position. Surly Singulator features CNC alloy body, variable chainline, floating tension pulley, stainless steel pivot bushing, Triple sealed reversible spring. Compatible with 1/8" and 3/32" chains. 11T jockey and slotted alloy chain rejection side plates. All in all... the mutts nutts of SS chain tensioners.