This threads on to the end of of the toggle clamp to make contact with the underside of your desk.
Legacy customers who purchased mounts prior to 2020 may wish to purchase these to replace their existing feet. These newer leveling feet are made of a solid phenolic plastic, and are much more rugged than the older version.
These feet have a 5/16-18 thread on them, so if you're purchasing these to use with your own home built mount, be sure they the threads on the toggle clamp match. Many other toggle clamps use M8 threads which would not be compatible.