anyone have this experience?

I have an RM20 which I love. HOwever I have a module that I cannot screw in as the left thumb screw just keeps turning. I took a thumb screw out of another module that works in the RM20 and the same thing happens. That module will screw perfectly into my RM50 and RM4.For some reason the RM20 just does not like that particular module. I can put the screw from that module into another module and it tightens right up. I am afraid to use the module with it not completely tightened down. If anyone has had this experience let me know.

The thumbscrews don't actually fasten to the modules, they only make the mounting connection to the amp itself and squeeze the module to the face toward the face of the amp via the head on the screw. It can only be one of two things: a stripped thread on your thumbscrew OR a stripped thread in the RM20's welded capture nut.

The test to confirm where the issue lies is a simple one. Take a few thumbscrews out of your modules, including the one you suspect. Visually confirm they are all the same length. This is important, as I have seen many replacement screws used in donors a touch too short. Then take each screw and try it in both holes of your amp (no module used here). Isolate where the issue is.

If the screws are bad, you buy replacements. If the problem seems to be the hole in the amp you can use a tapping set to try to re-thread the hole. If it's a bad stripping of the hole, you may need a hole filler and then tap it.

Also, as long as one side makes a solid connection the grounding to the chassis is achieved.

Glad to hear that I can still use it. It is weird. I know you gave two options but neither is right. The screw that is supposedly stripped will screw in if I take it out and use it in another module. And if I use a screw from another module in this one it still will not work. I know it sounds impossible and I swear it is the damnedest thing! The hole in the amp works with all other modules and screws. However if it still being grounded by the other screw, it is not an issue for me.

Is the faceplate or module chassis bent in any way so that the module won't mount properly?

EDITED twice so it appears I can speak English.

Thanks Drew. That is a good suggestion. I will check it later when I get home.

Or maybe the faceplate is a little thicker

Does the module easily slide all the way in and tightly seat firmly to the amp before the screws are tightened? I had a problem with a module not seating correctly (RM100LB) and it turned out there were wires hanging down inside the amp above the module port.

The module is seated all the way in. I am thinking that the faceplate must be slightly thicker or something on the one side. I have not had the amp at home in order to check it out since last week but have a few days off gigs now and will check on all of these things.
thx everybody

Update: I put thi mod in the bottom bay of my RM4 and it would not seat. So I took the module above it out and that way I could see the bottom module and it is slightly thicker and I could push it just right and voila, it seated. I can't see into the RM20 but as Rob said, it is ok as long as one side is seated.
Thanks everyone....
rick

Sometimes you can vary the number of washers between the front panel pots and the front plate to adjust the depth the the module's edge-connector fits into the chassis' edge-connector.