In the heat of the moment you will probably put the spacer into your jersey pocket . . . and, of course, forget about it when you throw your kit into the washing machine. So this will prevent that.
Also, the Race Clip doesn't grab 16oz cartridges very well, so the sleeve is an adapter for a more snug fit.
Printed in PLA so I don't know how it will be during really hot temps….
The author marked this model as their own original creation.