It is attached to the hole at the bottom part of the stem. On this special holder you are able to attach for example bottle basket, light or a cyclocomputer. Make sure you have the right model of the stem and that the stem has the hole in the bottom part. The top part of the holder is 22 mm in diameter.
Designated for KOSTKA SK2822 stems, which has a hole in their bottom part. You will not be able to mount this holder on the older versions of this stem. The hole is required. Made from steel. The top part of the holder is 22 mm in diameter.