Hi San Creative,
Thanks for the question. You're not missing a screw.
San Creative posted:
Please see the picture I uploaded for my L1 Model 2; am I missing a screw on the top hole?
There are three holes in the bayonet. There are two screw holes in the Cylindrical Radiator® top section and only two screws.
The reason for having two screws and three holes is to allow you to shorten or lengthen the length of the bayonet. This is a carry over from the original L1 design. There were only two holes, and two screws, and the bayonet extended farther. This meant you needed a little more ceiling clearance to set things up.
Does that help?
Always wondered that...