Aftermarket speedometer not working help!!

I bought a Mike’s XS aftermarket speedometer to do an Atari removal on my 82 xj750 well after getting it and trying it to the cable before ripping everything apart I took the speedometer cable off the back of the Atari the cable slides into the back of the aftermarket one but my question is:
Should the cable be a snug fit ? thr cable goes into the hole but if you can rotate the whole aftermarket gauge and it doesn’t attempt to spin the interior cable at all. Also examining the hole in the back of the aftermarket gauge it looks like a round hole but the interior of my speedometer cable is square.

I know people have gotten and replaced the Atari with aftermarket gauges from mikes XS before and had success so what am I missing ?

This is the gauge I got

https://www.mikesxs.net/2-5-chrome-mini-speedometer-w-black-face-trip-readout-g.html

 

The end of the cable should be a slip-fit, with little to no slop. If the cable socket for the gauge is round, then you have a faulty gauge and should contact Mikes XS for a replacement. Manufacturing errors do happen, and sometimes they don't get caught before a product is packaged for resale.