This is a simple vertical holder for a pen, pencil, or suitable tool. The holders can be attached to flat surfaces either by double-sided tape or fasteners such as screws or bolts.

A number of useful sizes are provided as STL files.

The parametric OpenSCAD file can generate multiple connected holders of various sizes.

A number of stl files are provided for use with pencils, pens, markers, and small :

Single, no holes (mount with double sided tape or glue)
Single, one hole
Single, two holes
Double, no holes
Double, two holes
Triple, three holes

Single, one hole, larger for markers such as sharpies

The OpenSCAD parameters are described in the file itself.