You've probably noticed there are dozens of methods/terminology for identifying snap sizes. Some refer to the size and/or length of the screw used to fasten the stud; others use diameter of the stud barrel - but is it inside or outside-diameter? We provide every possible measurement so you know what you're getting. But first, here are the (generally accepted) standard terms for the snap components and how they all fit together: The STUD is the base or bottom of the snap and has a raised rim with a lip on it called the barrel. The studs in this set are attached to wood, fiberglass or other solid material by galvanized steel screws (included). The SOCKET is the top-half of the snap and has a ring that's slightly larger than the barrel of the stud. To close the snap, the socket is forced over the barrel of the stud and makes a 'snap' sound (at least most agree on where the name came from!) The socket has a center hole and is attached to canvas or other material by means of a dome-shaped CAP with a hollow tube protruding from the underside. A small hole is cut/punched in the canvas/fabric where you want the snap located, usually with a hollow punch or other tool (not included). The tube of the cap is put through the hole from the top side of the fabric and then through the stud. The cap and stud - with the fabric between them - are permanently mated by rounding-over or flaring the end of the tube with a flaring tool or anvil & mandrel (not included). DIMENSIONS: Stud outside diameter .37", stud height 3/16"; flange diameter 9/16". Backing piece tube OD .15", tube length 3/16". Additional pieces available separately.