They go under the steering column where it attaches to the box.
They come in different thicknesses and most have 2 or 3 shims.
The preload is measured using a weighing scale attached to the steering wheel, before the steering box is put back in the car.

The factory workshop manual explains how they are used, and what they look like.
I replaced the bearings and reassembled my steering column using the book.

It adjusts the bearing preload on the column, because there is no adjustment for that axis.