This is a simple thing that slips over the end of the upper lever arm of a nail clipper, to give you a better grip. At least for me, it keeps my thumb from sliding down the lever arm, so it is easier to clip my finger nails. I was surprised at how much difference it made..

The OpenSCAD file is entirely parametric, but I think most nail clippers can be accommodated by changing just two input parameters, as explained in the OpenSCAD file.

The sketch (pdf file) shows at least most of the parameters and variables, and a very rough sketch of the thing. It's a scan of the un-cleaned-up sketch I used during the final design stage.