Spacers

Spacers fit on the steerer tube, between the top of the headset and the stem. They allow you to easily set and adjust the height of your bar/stem.

Most new bikes will come built with approx 30mm of spacers (in 5 or 10mm increments) which can then be positioned above or below the stem as required to achieve the ideal height.

Some riders prefer to "slam" their stem, with few or no spacers below it, as they feel it gives a more "Pro" look. It's ultimately an aesthetic choice - the fit will be the same either way.