The Beiter Tri-Liner is used to mark the exact position of vanes (like e.g. Spin Wings™, Kurly Vanes™, Rite Flite Vanes™, ...) on arrow shafts up to 7,2mm (9/32") Nock-out-diameter. With the Beiter Tri-Liner you draw lines exactly in the position you need. An exact orientation of nock and vanes is possible thanks to the adjusting ring on the back (pic.1) and the tabs on the ruler (pic.2). You decide the nock and vane position, as well as where to start and end drawing the lines. For both RH or LH, Recurve or Compound.