The hollow square hole design of the titanium alloy uses an integrated center shaft installation tool, providing a stronger structure compared to standard square hole designs. The center shaft features multiple waterproof seals for enhanced durability. The titanium alloy center shaft is fully hollowed out, and models under 800 use a titanium alloy hollow shaft for reduced weight and improved performance. The new design combines a titanium alloy hollow shaft with a 7075 aluminum alloy cup, using a one-piece shaft cup locking system for easier installation and a cleaner appearance. Rubber seals provide waterproof protection on both sides of the bearing, effectively preventing water ingress. The center shaft includes an aluminum alloy sleeve for improved waterproof performance and better overall texture. Color: Black Material: Titanium Alloy Package Contents: 1 x Square Taper Bottom Bracket for Brompton Note: Only the items listed are included. Lighting and display differences may cause slight color variations between the image and actual item. Measurement tolerance: +/- 1-3 cm.