For the Nikon 7200 you need a filter in the size 67 mm, this also applies to all lenses. 

Yes, I believe you can with any trail cam. There are several videos on YouTube. You need a 4.0x1.7mm plug. I saw one video that explains a direct hard wire. After watching some videos, I decided it was easier and about the same price to buy the Stealth Cam 12v external battery pack with solar panel. I paid $50 at Academy Sports online. Plus the 4.0x1.7mm plug from Amazon. But if you like to make things, there are plenty of videos on making your own solar battery packs. 

For this series, front thread diameter is bigger than the back thread diameter.
for example:
Back thread diameter (attach to lens): 40.5mm
Front thread diameter (attach additional filter/other accessories): 43mm
Variable ND filter size other accessories size

37mm	40.5mm
40.5mm	43mm
43mm	46mm
46mm	49mm
49mm	52mm
52mm	55mm
55mm	58mm
58mm	62mm
62mm	67mm
67mm	72mm
72mm	77mm
77mm	82mm
82mm	86mm

 

hell 37mm ND need 40.5 mm outside thread 

For this series, front thread diameter is bigger than the back thread diameter. for example: Back thread diameter (attach to lens): 40.5mm Front thread diameter (attach additional filter/other accessories): 43mm ND FILTER size front thread 37mm 40.5mm 40.5mm 43mm 43mm 46mm 46mm 49mm 49mm 52mm 52mm 55mm 55mm 58mm 58mm 62mm 62mm 67mm 67mm 72mm 72mm 77mm 77mm 82mm 82mm 86mm