DIN 6798 V Countersunk Serrated Lock Washers have twisted tab type serrations around their periphery and a 90° conical bearing surface. They are designed for countersunk holes and are used with metric flat and oval head screws (inch series screws have an 82° head angle so they aren't compatible). Spring steel, in zinc plated and plain finish (without a rust protective coating), is available. Match the washer size, which is its nominal hole size, to the size of the screw; to illustrate, match an M6 washer with an M6 screw. They are sometimes listed as DIN 6798 Type V.