I've used these before and just installed them on my battery terminals (6mm). They're called Nordlock washers and are probably the best anti-vibration lock washer you can get. Typically found at specialty hardware stores and online.
	
	
		
			
				
					
						 
					
				
			
			
				
					
						
							 www.nord-lock.com
						
					
					www.nord-lock.com
				
			
		
	
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				NORD-LOCK® WASHERS
Wedge-locking security for bolted joints exposed to extreme vibration and dynamic loads.
				 www.nord-lock.com
						
					
					www.nord-lock.com
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