Package includes 20 pcs kits and 20 pcs water proof O-rings, it makes the rivets durable in the deep water when use with the O-Rings Aluminum body with aluminum mandrel, all aluminum No plastic; Corrosion-resistant and good stress makes you convenient and save , A tool is required for installation ( Tool not included) Size of hole is 5mm, head of rivets is about 10mm, black part is 2.5cm, Detail measurement look for the 3th picture -Grip style, Back side spread out in 3 directions to hold the materials together and make strong enough for mounting accessories such as a rod holder These kayak rivets widely used in shipbuilding, containers, industries aviation, automobiles, furniture appliances and more; they work great on many applications on kayak like as handles, pad eyes, rod holders, etc. Colour: black Material: metal Size: 5.9cm Package Contents: 20 x kits 20 x waterproof O-rings Only the above package content, other products are not included. Note: Light 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.