Check the listing for details. AltaLine Bicycle Conversion Kit Crank Bike Bottom Bracket Kit Black or Chrome.. Condition: New. Listed at 15.89 USD. Specifications: Shell Width:68mm: This conversion kit is designed to fit American-style bottom bracket shells with a width of 68mm, which is commonly found on cruisers, BMX, and vintage bicycles. Spindle Type:SQR JIS (Square Tapered Japanese Industrial Standard): The spindle features a square taper interface, making it compatible with a wide variety of three-piece cranksets. This type of spindle provides a secure fit and is commonly used in modern cranksets. Cup Material:Steel: The cups are made from steel, offering a durable and sturdy foundation for the bottom bracket. Steel is resistant to wear and provides strength under pedaling forces. Threading Interface:24 TPI (Threads Per Inch): The cups are threaded at 24 TPI, a standard for American bottom brackets, allowing a secure fit in the bottom bracket shell. Spindle Length Options:128mm, 132mm, or 136mm: This conversion kit is available with different spindle lengths to accommodate different crank arm setups. The spindle length determines the chainline, which must be correct for multi-speed bikes or chain-driven systems. Spindle Material:Chromoly: The spindle is constructed from chromoly (a strong steel alloy composed of chromium and molybdenum), known for its durability, strength, and resistance to bending under heavy load. Color:Available in Chrome or Black: The chrome finish adds corrosion resistance and a shiny aesthetic, while the black option provides a sleek, understated look. Conversion Function:Converts American Style 1-Piece to 3-Piece Cranksets: This kit allows you to upgrade from an older one-piece crank (often seen on American cruiser bikes) to a more modern three-piece crank system. This conversion is common on cruiser bikes, vintage BMX bikes, and other American bottom bracket bikes.Brand & Manufacturer:Brand: Alta, a reputable brand known for producing high-quality bicycle components, particularly for custom bikes, cruisers, and BMX bikes.Manufacturer: F&R Cycle Inc., a leading manufacturer specializing in parts for lowrider, cruiser, and custom bicycles.Components Included: Spindle: Available in 128mm, 132mm, or 136mm length, made from durable chromoly steel with a square taper JIS interface. Bearing Cups: Steel cups with 24 TPI threading, designed to press into the bottom bracket shell of American-style bicycles. Ball Bearings: Bearings that ensure smooth crank rotation during pedaling. Dust Covers/Seals: Dust covers or seals to protect the bearings from dirt and moisture, improving longevity and reducing maintenance needs. Lockring and Retaining Hardware: Hardware to lock the bearing cups into place securely.Functionality: One-Piece to Three-Piece Crank Conversion: This kit enables the conversion from a one-piece crank system (common in vintage or cruiser bikes) to a modern three-piece crank system, offering improved pedaling efficiency, smoother performance, and easier maintenance. Customization Options: The different spindle lengths allow the rider to choose the correct length for their specific bike, which helps in maintaining the ideal chainline for the drivetrain.Applications:Cruiser Bikes: A common upgrade for cruiser bikes that originally came with one-piece cranks but can now use a three-piece crank system.BMX Bikes: Frequently used to convert older BMX bikes with American bottom bracket shells to a more modern three-piece setup.Vintage/Classic Bikes: Ideal for upgrading classic bikes with outdated bottom bracket designs.Custom Builds: Excellent for custom-built bikes where a modern three-piece crank is desired.Advantages:Improved Pedaling Efficiency: A three-piece crank system is more efficient than a one-piece crank, offering better power transfer and a lighter overall weight.Durability: Chromoly spindles and steel cups provide excellent durability, suitable for both recreational riding and performance use.Compatibility: Works with American bottom bracket shells and modern cranksets, allowing for a wide range of three-piece crank arms.