Promax EX-1 Alloy external Sealed Bottom Bracket 68/73mm BlackPromax EX 1 Alloy external Sealed Bottom Bracket 68 73mm Black. EX 1 External bottom brackets feature cold forged and CNC machined alloy cups dual labyrinth bearing covers and precision sealed bearings. They are the perfect match to Promax CF 2 and HF 2 cranks and ultimate upgrade to the budget BBs sold with most crank sets. Fits all 24 millimeter bottom bracket spindles and frames with 68 or 73 x BC1. 37 bottom bracket shells TECH SPECS Bottom