Special washer with a square hole. Designed for use in wood with carriage bolts or other similar bolts. Prevents carriage bolt from spinning when nut is tightened. Made of zinc-plated steel. Carriage bolt washers. BOX DISCOUNT - Buy a full box and get a discounted price. See "Quantity Discounts" for box quantities and prices. Buy online and have it shipped direct to your door. All items also available in our store in San Diego. Click "Contact Us" at the bottom of this page for store location and hours.