30.9mm to 31.6mm steapost conversion shim. Looking to fit your fancy carbon post or dropper to another bike frame but just found out your frame is too big and your seatpost too small? We've been there too, this is what you need.
If you've got a few bikes in your stable or are forever swapping parts between bikes then this is a godsend. Perfect for fitting your skinny dropper post to your new fat tubed frame.