Wiggly Phoropter

[Neophyte Optician]

I have a phoropter that is wiggly at the neck. No matter how tightly I tighten the silver knob at the top, the phoropter wiggles freely. I've tried uploading a picture, but the system keeps saying that the upload has failed. Any ideas as to how I can fix the wiggly phoropter in the office? Thanks.

[Howard Gorin]

What is the make and model of the instrument?