Back Up Ring Vs O-Ring. The contoured face is the one.
        
         
        
        from www.mercergasket.com
    
        
        The contoured face is the one.
    
    	
            
	
		
	
        
    Gasket vs. ORing Differences and Common Applications Mercer Gasket
    Back Up Ring Vs O-Ring The contoured face is the one. The contoured face is the one.