This beam compass is designed to fit the smallest pencil up to a standard Sharpie. The pencil holder is press fit on a 1/2" dowel, and a small screw could be added if necessary.

needed to complete : 1@ 1/2" wood dowel 2 @ 5mm x 35 length or longer hex bolt 2 @ 5mm wingnuts 2 @ 5mm nuts 2 @ 5mm thumbscrews 1 @ 1" or longer bugle / gold screw

I designed this compass after using poorly designed beam compasses for 20 years from hardware stores that either cracked or didnt hold the pencils/pens correctly.