The Hillman Group 300045 Split Lock Zinc Washer 1-Inch 10-Pack

"Engineered to provide more uniform load distribution, split lock washers are great for any indoor/outdoor project. Ideal for situations where potential loosening from corrosion or vibration is a concern, split lock washers are used to prevent nuts and bolts from coming loose. These fasteners contain split ends that help ""lock"" into the mating material, thus providing a locking feature when tightened beneath a nut. The zinc finish provides moderate corrosion resistance. Use with treated lumber in applications with like nuts and bolts of similar diameter. *".