Problem Solvers Bushnell Eccentric Classic Bottom Bracket - 68mm x 54mm BLKProblem Solvers Bushnell Eccentric Classic Bottom Bracket 68mm x 54mm Black. The Problem Solvers Bushnell Eccentric Bottom Bracket is the industry leading design for chain tension adjustment on tandem and dedicated single speed bikes equipped with eccentric bottom bracket shells. The classic version features full body aluminum construction across the shell for maximum surface area friction and additional value. Accepts English threaded bottom bracket