This set uses a one piece, 'self backing' grommet: when you crimp the grommet, the barrel is rounded-over to create the backing - no separate backing piece needed. This makes it easy to attach 1/4" grommets (small grommets are sometimes referred to as eyelets) to a wide variety of materials - outdoor canvas or vinyl covers, nylon or leather purses & luggage and more. Barrel length 3/16". Additional grommets available separately. Excellent quality - made in Taiwan.