3/8" x 7/8" OD Plain Finish 18-8 Stainless Steel Flat Washers, 100 pk.: Amazon.com: Industrial & Scientific
Small Parts Steel Flat Washer, Zinc Plated Finish, DIN 125, Metric, M20 Screw Size, 21 mm ID, 37 mm OD, 3 mm Thick (Pack of 25): Amazon.com: Industrial & Scientific