Plastic composite 1/2" crown 19/20 gauge staples are manufactured with a blend of polymer resin and fiberglass - 100% steel and metal free. These 19/20 gauge composite staples work exclusively with the Spotnails MT19/12. Spotnails plastic composite staples will not degrade in sunlight or high heat conditions. These plastic staples are ideal for boat building, casket manufacturing, timber processing and more.