Race Number Adaptor Seat Post Mount which also uses the SP0048

which also uses the SP0048 Aero post

Bontrager/Trek Flare RT / Trek CarBack*

3D printed seat post mount perfectly dimensioned for the Argon 18 E-119

Specialized Stix Elite (Horizontal - image pending)

Race Number Adaptor Seat Post Mount which also uses the SP0048With a Concentric Cycling Race Number Adaptor, you'll always be ready for race day. Simply remove your tail light and replace it with your race number. No tools or rubber bands needed. To use the adaptor, simply slide in your race number, click in the tool free locking mechanism and insert twist the holder into your Concentric Cycling Seat Post Mount. When the race is over, you can replace your race number with your Radar, Camera or Tail Light in