Lock Washer, Lock Washer Type External Tooth Lock, Finish Plain, Material Stainless Steel, For Screw Size M12, Inside Diameter 13 mm, Outside Diameter 20.5 mm, Maximum Thickness 1 mm, Dimensional Standards DIN 6797, Material Grade/Class 18-8, Pack Size Small Pack, System of Measurement Metric, Package Quantity 25 Use Open Perimeter External Tooth Lock Washers with round head, pan head, and binding head screws, or similar fasteners whose heads are large enough to make contact with the washer teeth, to help minimize fastener loosening.