The Hillman Group 290250 Number-8 x 1/2-Inch - OD Bonded Neoprene Washer, 100-Pack Used to prevent leakage, distribute pressure of the bolt or screw and also make a great cushioning agent to help with vibrations Applications include aircraft, auto, marine, railroads and railroad equipment, And more applications mobile homes, air conditioning, hydroponic structures, outdoor signs and many more Zinc-plated for moderate corrosion resistance