I just used Goop on my helmet. The helmet I made for MandalorFett, I put some screws in. I drilled holes in the helmet first, then I put the ears on, marked where I should place the screws, then drilled them big enough so the head would fit. Then I put the screw in and JB Welded it in place, so you could place the ear on, then use a nut to tighten it in place.