The hollow square hole design of the titanium alloy is compatible with an integrated mid-shaft installation tool, providing enhanced structural integrity compared to standard square hole designs. The mid-shaft features multiple waterproof seals for increased durability. The center of the titanium alloy shaft is fully hollowed out. Shafts within the 800 series feature a hollow titanium alloy core. This model features a new construction combining a titanium alloy hollow shaft with a 7075 aluminum alloy cup, offering a unified spindle and cup structure for improved convenience and aesthetics. Rubber seals provide waterproof protection on both sides of the bearing, effectively preventing water ingress. The mid-shaft includes an aluminum alloy sleeve for enhanced waterproof performance and improved finish. Color: Black Material: Titanium Alloy Package Contents: 1 x Square Taper Bottom Bracket Note: Light and display settings may cause slight color variations between the image and the actual item. Measurement tolerances are +/- 1-3 cm.