They clip on with 2 rubber straps with holes in, onto 2 clips on each arm.  So 8 straps in total.  I fitted them in about 5 minutes but they need a little tweaking in good light before I use them.  They have standard adjusters similar to these.
	
		
			
		
		
	
		
		
	
	
	
		
			
		
		
	
In fact they they are very like these though they have 2 straps on each side and don't have the clip at the top of the mudguard.