- 1/4" BSP Copper Washer - pack of 3. This washer is suitable for use in 3 places - the Drive Side One Way Valve and the straight through breather or unions fitted to SOHC crankcase fittings and cambox. These washers are not quite as wide as item 0090b, and therefore look less obtrusive when fitted behind these unions (you may decide though you prefer to fit red fibre washers which we also sell). These can also be fitted to 1/4 BSP petrol taps. Sold as a pack of 3