Fasteners for Hope operators

A home owner from USA says:

I ordered a 39-353 Hope casement operator a while ago to try out as a replacement for our original 1950s Hope operators. (Most of them still work, so we have some good ones to compare the replacement with, but there are a few that no longer crank and we're hoping to get those windows working again.)

The operator is definitely the correct fit for our windows in terms of screw spacing, arm length and style, etc. The problem I'm running into is that the installation screws don't tighten fully - they go in all the way and then just keep spinning, which leaves the operator wobbling when we turn the crank.

We wondered if the screws that came with the part maybe weren't long enough to catch (the base of the replacement part is thicker than the original, which has much shorter screws that sit flush in the base and still work great), but trying longer screws did not help.

Is this something you've run across before with these parts? Any suggestions?
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Dave Sr. from SWISCO responded:
I'm not sure what the problem might be. The 39-353 operator base has two holes which the screws pass through. The frame on the window should have threaded holes for the screws to mount into. I would suggest going to a local hardware store and getting the proper length and thread count to go with your window. Another issue could be that the thread in the window frame might have become stripped, whihc would explain why you can't tighten down the operator.
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