I'd have to agree with northwind, the motoslider crash bungs are the ones to get, just like northwinds pic below! I have seen a couple of bent R&G ones now, and have to say I wouldn't use them.
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I wouldn't recommend the type that fit to the front cylinder mount either, too weak and will bend or snap even quicker than R&G
So will the rear cylinder mounted ones too....
From an engineering/strength view only the main frame mount should be used, from a marketing view its all about easy fitment and for that you would go for the lower quality cylinder mount ones (which are virtually all of them)
Go with the Motosliders or a JHS Racing set as they use the same mounting point.
www.motosliders.com or
www.jhsracing.co.uk