It's . 12mm in inside diameter. The punch measures 96mm Long, the mandrel is 94mm long, the die bottom die measures in 20mm in diameter, and the rubber hammer is 250mm long. Everything is sorted in a clear storage case for easy storage and carry. The grommet kit has a smooth and no edges, so there is no risk of scratching clothes or even people. The 2 parts fit well so that you don't have to worry about it falling off, it stays firm even in washing machines or high-intensity exercise. The eyelet tool is made of metal, which is sturdy and . It is weather , not easy to rust, and can be used for a long time. The grommet tool come with 3 non-slip designed installation tools allowing make you easy to install by yourself. After punching holes in the leather with the included punch, hit the two parts with a hammer to fit them. The grommet tool kit can be used for DIY leather crafts, canopy or fabrics, repairing and decorating shoes, bags, clothing, sunshade, curtains, belts, hats, jeans, jackets, etc, or you can punch holes in books, cards. Colour:As Shown Material:Metal Package Contents: 1 set x eyelets and grommets Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.