FSA BB-4000 Omega Drive Mega Exo Bottom Bracket: Replacement bottom bracket for FSA Omega Drive cranks. The Bottom bracket is a key component to every chainset. Smoothness movement is critical, yet must be balanced by enough sealing technology to sustain a reasonable lifetime of use. FSA Mega Exo bottom brackets are the result of years of development, & feature exclusive innovations to guarantee the best balance of efficiency & durability. FSA use the state-of-the-art materials like Silicon Nitride formed ceramic ball bearins, or highly polished chrome steel ball bearings, depending of the level of the bottom bracket. Oversized cartridge bearings Forged steel & CNC machined external cups Composite centre sleeve with double o-ring seals Weight: 97g