This one holds a range of diameters, which especially helps to hold fat markers. It accommodates an m5 nut internally to make adjustments less fiddly.

70-80% rectilinear infill, PLA, 0.15 mm layer height
need 35-45mm m5 or 1.5" #10 flat-head machine screw. File two flats on the head so it measures 7mm flat-to-flat. Screw it together with nut, washer, and thumb nut.

Point can be 2mm-5.5mm diameter. A sharpened nail works nice.

File or sand the wedge so it's smooth. Trim it to length if you like.

The pivot is much smoother to adjust if you file the sharp edges (where it sticks to print bed) and scribble some graphite/soft pencil onto the touching conical surfaces..

EDIT: clamp_without_index_holes.stl is variation of clamp.stl if you are having trouble printing first layers. You only need one or the other