@etcswjoe, Joe I went with the 5mm scope end to be sure it would fit thru the smaller "D" plug hole. Maybe grab a D plug and measure its diameter at the bottom of its threads to be sure OR grab a nut that the D plug will screw into and measure its I.D. to be sure. If you havent got the tools to do so and want me to do it for you just let me know and I would be happy to. It looks like the scope you are looking at has an 8mm head on it, they may work but not sure. It seems like years ago I went thru what you are going thru and found the 5mm to be the better choice. Its always something! TTYL (I learned that today from @COWBOYBILL and now know it means Talk To You Later - who says an ol pea brain like my cant learn something new LOL) Your ol riding buddy, PUC
P.S. - the one you are looking at does look like a dandy though! I REALLY like the 16 foot cable.. I spent the xtra and went with 25 feet on mine to be able to use it for looking inside duct work but 16 feet is worthy!