Adjustment Valve Won't Tighten


I have used my new smith little torch a few times and suddenly a problem popped up. I went to turn on my tanks today and the adjustment valve on my oxygen regulator won’t tighten. I switched the valve and it still won’t budge more than two turns. It comes to a complete stop. I have checked inside and there doesn’t seem to be anything blocking it’s path. I’ve used other oxygen/acetylene systems before (I was trained on them) but this is the first I’ve ever seen this happening.

Has anyone had this happen? I called the local gas and welding company and they had never heard of it happening either and said I may have a faulty regulator. I’ve googled my heart out today and had no luck!

Thank you so much for any help!