Network Cable Tester Ensures Continuity RJ45/BNC Compatibility

I'm need to move my Xfinity router; it uses coaxial type cable which I understand is BNC. My home has this type cable pre-installed in each room by DirectTV (no longer in use) and my Xfinity installer used his coaxial/BNC tester to install the Xfinity router in an upstairs room (I need to move it downstairs). I have experience with installing RJ45 & Cat6 Ethernet cables (and have a tester for such), yet never a coaxial/BNC cable. I purchased & received my Pyle Network Cable Tester PHCT45 from Amazon specifically for this type cable and tried to test yet none of my coaxial/BNC cables will fit onto the tester's ends -- the tester's "metal ends" are larger than my all of my coaxial/BNC threaded cable-ends (assumed it is all the same size!). What am I missing; how can I make this tester work or should I return it to Amazon?

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