Problem Solvers Bushnell Eccentric Lightweight Bottom Bracket - 68mm x 54mm SilverProblem Solvers Bushnell Eccentric Lightweight Bottom Bracket 68mm x 54mm Silver. 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 lightweight version features additional machining and drilling of the alloy body to reduce weight. Accepts English threaded bottom bracket cups (1. 37 X 24 tpi)