Package of 50 premium washersInside Diameter 3/8"Outside Diameter .68"Thickness 3/32"304 stainless steel for corrosion resistanceLock washers are commonly used in applications involving vibration and possible slippage of fasteners. Industries that commonly use lock washers are transportation related (automotive, aircraft & marine). Split lock washers are also called helical spring lock washers. These are made out of a spring coil that cut or split. This makes it so the two ends of the coil forced outward to the mating surface so when the washer is fastened each end of the coil will bite into the surface of the head of the screw and to the surface to which you are fastening.