Simple, u turn the plastic bracket around, fit the sq plastic in the other way, then get a wall bracket and pipe and mount your unit on the pie and finally on the wall 

yes, on both sides of the filter 

I have a sigma 18-35mm f1.8 art series, it should fit if you have the same one 

The adapter will mount the lens and you will be able to use it manually. However, my copy of the adapter does not allow the lens to be fully mounted all the way until it clicks into place. It doesn't quite make it, but it's still very solidly mounted. Also, the manual aperture linkage doesn't work properly (on my copy, at least) so exposure is controlled only by shutter speed and/or ISO. You will be able to manually focus and zoom the lens but no VR, of course. It will be a frustrating experience. Instead, get a 14-140 Panasonic zoom if you can afford it! 

Hi, we checked the Sony a6600 18-135mm lens seems 55mm, if you like this filter, please reconfirm the lens size, the 55mm lens need to order 55mm size filter,thanks.