UPDATE: I added variations with different heights: 20mm, 25mm and 30mm. I you find this useful but need a specific height, let me know. I can change the model to suit what you need.
This is a 28mm tall stem spacer for a 1 1/8th steerer tube that I made for my Specialized SL2, However, it should be able to fit on any 1 1/8th stem.
I would print with at least 20 %. I have many miles on the bike with the spacer and no issues.