The Astro Tools RS14 50pc 1/4-20 Steel Rivet Studs are zinc-plated steel rivets with a #1/4-20 thread pitch. They have an outside diameter of 8.9mm and require a 9mm (23/64") drill hole. With a length of 13.7mm and an overall length of 27.5mm, these rivets are designed for heavier-duty fastening applications.