The Regulator Yoke Washer with Rubber Ring is for use with oxygen regulators. It is fit between the regulator and the oxygen tank to create a seal with the oxygen tank.  
 
Constructed of brass and viton for durability and optimal performance
Makes airtight cylinder-yoke connection easy to achieve with little force
Never install a regulator with more than one regulator yoke washer at once
Should be replaced every 6 months or in the event of a leak