Also known as Sems screws, these screws have a permanently attached but freely rotating tooth lock washer that grips the screw and your material for vibration resistance. When a wrench won’t fit, turn these screws with a slotted screwdriver instead. About half as strong as medium-strength steel screws, these screws are best for light duty fastening applications, such as securing access panels. They have a zinc plating to help prevent corrosion in wet environments. They meet ASME specifications for dimensions and SAE specifications for material quality.

External-tooth lock washers have sharp teeth around the outside edge that bite into the screw and the material they’re installed on. They have more holding power and vibration resistance than internal-tooth lock washers. Screws with these washers do not have a flange, so length is measured from under the head.

Internal-tooth lock washers have teeth along the inside edge and a smooth outer edge. They have a more finished appearance than external-tooth lock washers, and they’re less likely to damage your material. However, they have less holding power and vibration resistance. Screws with these washers also have a flange. Their head height includes the flange; length is measured from under the flange.

Match the thread spacing of mating components. Coarse threads are the industry standard; choose these screws if you don’t know the pitch or threads per inch. Fine threads are closely spaced to prevent loosening from vibration.

Certificates with a traceable lot number are available for these products. Download certificates from ORDER HISTORY after your order ships.