Extendable desk tightening screw function broken
I have a sitting/standing desk, which should allow me to change the height of the desk. The design of the desk is one pole attached to the legs, which has a thinner pole inside it, which is attached to the flat desk surface. The screw which holds the inside pole attached to the flat desk surface in place seems to have worn down so that it can no longer hold the pole in position (I now have the desk propped up with yoga mats on each side). For a while, I stuffed some card inside the screw and it fixed the issue, but it has now stopped working - instead, the screw just turns endlessly without ever tightening against the inside pole (attached to the flat desk surface). Both screws (one on each side) are now broken.
What is this ‘tightening screw’ piece called and can I replace it myself?