Prototipo Works

Prototipo Works - Under Flush Bidon Cage Boss Blank 5.5mm (Black)



Prototipo Works M5 6061 Aluminium Alloy Underflush Bidon Cage Boss Blank. 3mm M5 Metric thread. Excellent finishing touch to all builds.

Used to neatly and professionally blank bidon cage bosses when not in use. Designed to visually disappear under flush in most bidon bosses.

Designed and engineered in Melbourne, Australia.


Features Narrow head allows it to disappear in most bidon mounts
Taper Tech thread base for easy installation
Precision CNC machined from 6061 Aluminium Alloy
Precision laser etched Prototipo Works logo
Sold as pair 
Finish Natural CNC machined finish sand blasted matte
Hard anodised black.


  • Prototipo Works strongly recommends the use of a lithium based anti seize assembly lubricant during the installation of our hardware. An anti seize assembly lubricant helps prevent seizing, galling, cold-welding, and the fusing of metal on metal threaded components. Ideal for salty environments, humid environments, in the presence of water, moisture, sweat and ingress.

  • Please ensure all mating threads and installation tools are the correct size, are clean, free of damaging burrs and inserted straight.


  • Bidon cage boss hole opening diameter must be at least 5.6mm or greater (our under flush bolt is 5.5mm in diameter) with at least a 3mm unthreaded depth before the thread begins into the frame.

  • Where appropriate, we also offer a suitable version for a 5.1mm opening hole diameter or greater (our alternate under flush bolt is 5.0mm in diameter).

  • If unsure if it will fit correctly on your bicycle, please contact us.

Special Note: 

Prototipo Works engineer custom products and therefore appearance may vary slightly. 

Please ensure all mating threads are the correct size, are clean, free of debris and damaging burrs. Please ensure adaptor is aligned and threaded onto the valve straight and as intended.

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