Bike Seat Mast Cap Carbon Round Mast for Trek Road Frames - Bontrager

Bontrager Madone Carbon Seatmast Cap 128mm 5mm Offset Matte Onyx

Genuine Bontrager carbon seatmast cap originally designed for select 2018 Trek Madone road frames with round seat masts. Features a 128mm length, 5mm offset, carbon head, aluminum saddle clamp, and Matte Onyx finish.

Product Details

• Brand: Bontrager
• Product Type: Carbon seatmast cap
• Original Application: Select 2018 Trek Madone road frames
• Mast Profile: Round
• Length: 128mm
• Offset: 5mm
• Head Material: Carbon
• Clamp Material: Aluminum
• Clamp Design: Two-slot seatmast-cap design
• Saddle-Rail Compatibility: 7mm round rails with the appropriate clamp ears
• Finish: Matte Onyx
• Hardware Color: Black

Compatibility

Intended for select Trek road frames requiring a 128mm-long, 5mm-offset carbon cap for a round seat mast. This cap is not compatible with every Trek Madone, as different generations may use different mast shapes, lengths, or clamp systems.

Compare the mast profile, insertion dimensions, length, offset, clamp design, and finish with your original seatmast cap before purchasing.

Saddle-Clamp Information

The standard clamp configuration is intended for conventional 7 x 7mm round saddle rails. Saddles with oversized or oval carbon rails require compatible rail-specific clamp ears.

Installation Notes

Inspect the carbon mast and seatmast cap for cracks, crushing, or other damage before installation. Clean the mating surfaces, use carbon assembly compound when specified by Trek, and confirm that the saddle-clamp ears match the saddle rails.

Trek specifies a 6–8Nm tightening range for the seatmast clamp bolt on this round carbon system. Use a calibrated torque wrench and follow the service instructions for your exact bicycle.

What’s Included

This item comes exactly as pictured. Please review all photos for the included components, mounting hardware, packaging, and condition.

Alternative saddle-rail clamp ears, installation tools, carbon assembly compound, and additional components are not included unless pictured.