Twin-Pin Board Edge Center Marker
Two 6 mm steel dowel pins press into 6.05 mm bores 100 mm apart, with a pencil clamped exactly halfway between them. Set the pins on either face of a board up to 94 mm thick, twist until both pins touch, and slide it along to draw a true centre line. The 8.2 mm pencil bore has a 2.5 mm split and an M3 pinch screw with a captured nut, so it grips pencils from about 7.4 to 8.2 mm. The bar is 120 x 24 x 12 mm.
tool woodworking marking-gauge center-finder