The Problem Solvers Seatpost Shim is what you need when your seatpost is a little too small-diameter to fit tightly into your frame. It's made of light, durable aluminum and has a lip on the top so it won't slide down inside the frame during installation.
Length: 100mm with 3mm lip
|2.8mm shim, 27.2 seatpost to 30.0 frame||708752011502||ST0228||18007|
|0.7mm shim, 30.9 seatpost to 31.6 frame||708752077386||ST0250||13599|