For this 77mm ND filter，the lens cap/hood should be 86mm. 

1pcs magnetic attachment ring, 1pcs magnetic ND filter, 1pcs magnetic lens cap; 

sure. it could mount a 1/4 for gopro. 

If you rotate your ND filter past the ‘Max’ mark on the filter rim, it can cause an x-pattern, so ensure you’re not over-rotating. Variable ND filters also have limited application with wide angle lenses (they can only be used to about the halfway mark of Min and Max markings because the field of view is so broad). For a wide-angle lens, we suggest using fixed ND filters or ND2-32 or ND8-128. You can also try adjusting your focal length and reducing the density (rotating back towards the ‘Min’ mark) until the colour shift disappears. 

Not exactly sure about that lens, but don’t get this version, if you does fit. Get the their no “x” version that they offer for that lens. Not sure why this sell this Style when they offer a better one. Found that out the hard way.