A simple clip which is designed to snap onto something cylindrical. This is one of the most boring things I have ever made, but my wife needed one to hold her lather thingy. 

The inner diameter of the clip is exactly 20 mm in diameter, but you can of course scale it up or down to fit your needs. If you want it to fit a little tighter, scale it down so the inner diameter is slightly smaller than the object on which it will be clipped.

In the photo, I printed the clip in PETG with lots of perimeters so that it came out completely solid. I scaled X and Y to 98% and Z to 75%. It fits nicely on my shower head pipe which is 19.8 mm wide. Please excuse the gross hard water stains.

You can make advanced adjustments, such as increasing the thickness or making the clip longer or shorter, by tweaking this parametric model in OnShape:

https://cad.onshape.com/documents/44be10ecaf9c57f829ce262f/w/58c0394c37d147a07aa99a40/e/d45dcc787b32315600eed88c?renderMode=0&uiState=61fa0f32168a0f2540c86d31