The hollow square hole design of the titanium alloy is compatible with an integrated middle shaft installation tool, providing enhanced structural integrity compared to standard square hole designs. The center shaft features multiple waterproof seals for increased durability. The titanium alloy center shaft is fully hollowed out, and models within 800 series feature a hollow titanium alloy axis. The new design combines a titanium alloy hollow shaft with a 7075 aluminum alloy shaft cup, using a one-piece shaft locking mechanism for improved convenience and aesthetics. Rubber seals provide waterproof protection before and after the bearing, effectively preventing water ingress. The middle shaft includes an aluminum alloy tube sleeve for superior waterproof performance and enhanced texture. Color: Black Material: Titanium Alloy Package Contents: 1 x Square Taper Bottom Bracket for Brompton Note: Only the items listed above are included. Note: Lighting and display differences may cause slight variations in color between the image and the actual item. Measurement error allowance is +/- 1-3 cm.