There are two models here. One with 4 screw holes, one with two. Depends on how you intend to mount it in between the seams of the tiles. The holder part is tapered and is in a 45 degree angle from the wall. The top openening is around 21 mm, the bottom one around 17 mm. It is snug for my hans grohe showerhead.

Primary usecase for me is when trying to shower my kids/baby.