These markings are as close to actual measurements as we can make them! Use tape to line up each stamp to create longer and longer line measurements! Each increment is 1mm, so if you line up (2) 4mm stamps, you will have 10mm! If you line up (2) 9mm stamps, you'll have 20mm! Shank size: 1/4", 1/2" Stamp length: 4mm, 5mm, 9mm, 10mm The 4mm and 9mm stamps are designed to be used as repeating stamps; for example, you can use tape to line up the 4mm (or 9mm) stamp several times in a row to create a full, continuing line measurement to mark a long line. The 5mm and 10mm stamps have beginning and ending lines, so you would likely only hammer each of these stamps one time for one measurement.