BOX ONE CASSETTE SPACER KITS

Product Overview

The Box One Cassette Spacer Kit is a set of CNC-machined aluminum spacers designed to adjust the lateral position of the cassette cog on Box-branded cassette hubs. Extruded from 6061-T6 aluminum with a minimalist design, these spacers allow precise cog alignment for proper chainline adjustment. Each kit includes four spacers in different thicknesses for a total adjustment range of 1mm to 10mm.

Key Features

• 6061-T6 aluminum construction – CNC-machined from extruded aluminum alloy provides strength while keeping weight minimal
• Multiple thickness options – Kit includes 1mm, 3mm, and 5mm spacers that can be combined for precise chainline adjustment
• Minimalist design – Lightweight construction reduces unnecessary material while maintaining function
• Hub-specific compatibility – Designed specifically for Box One (Harmonic) and Box Three Pro and Mini cassette hubs

Technical Specifications

• Material: 6061-T6 aluminum, extruded and CNC-machined
• Spacer thicknesses included per kit:
  • Two (2) x 1mm spacers
  • One (1) x 3mm spacer
  • One (1) x 5mm spacer
• Total adjustment range: 1mm to 10mm (when stacking multiple spacers)
• Hub compatibility: Box One (Harmonic), Box Three Pro, Box Three Mini cassette hubs
• Sold as: Pack of four spacers

Compatibility and Ideal Use Cases

These spacers fit only Box-branded cassette hubs—specifically Box One (also called Harmonic), Box Three Pro, and Box Three Mini hubs. Not compatible with Shimano-spline hubs, oversized spline hubs, or other hub brands. Verify your hub is a Box cassette hub before ordering.

Best suited for riders using Box cassette hubs who need to adjust chainline for optimal drivetrain alignment. Proper chainline (straight alignment between the front chainring and rear cog) reduces chain wear, improves shifting efficiency on multi-speed bikes, and minimizes drivetrain noise and friction. On single-speed BMX bikes, correct chainline prevents chain rub on the chainstay and ensures even chain wear. Use spacers to move the cog left or right on the freehub body until the chainline is straight when viewed from above. Stack spacers as needed—for example, use both 1mm spacers plus the 3mm spacer for a total of 5mm adjustment. Ideal for riders building new wheelsets, swapping frames with different chainline requirements, or fine-tuning drivetrain performance. Check chainline adjustment after installation and verify the cog lockring threads fully onto the freehub body with spacers in place.