The plastic washer on the Spectra in-ceiling back boxes that holds the lower dome in place may be too big. the original size was .150 inch hole and there was some that were sent out with .250 hole because vendor sent the wrong pieces and they were mis-labeled. This may allow the washer to fall off if overtightened when installing. Please look at Image 1 for a bad washer and Image 2 for a good one, you can see the gap from the screw and washer.
Note: Click on the image to enlarge.
Image 1: Bad Washer
Image 2: Good washer
Pelco Cameras, Pelco Video Management
All models of Spectra in-ceiling back boxes. Analog Spectra's, and Spectra HD's
The hole in the plastic washer (clip) for the back box may have been drilled out to large (.250) and the screw may go thru it if tightened too much.
Do not over tighten the screw, use the safety lanyard and make sure when tightening the mounting screw that you push the plastic washer to the outside as in Image 3
Image 3: Do not over tighten the screw
Ensure the Snap-Cap washers are pushed outward upon tightening. This ensures a secure lower dome attachment.