If you've ever sworn, cursed and blasted at those STUPID plastic filler caps on the Disco II diff filler hole you might be interested in an alternative...
X-Eng's
X-Cap is a direct replacement, won't mank up as soon as you put a metal tool anywhere near it, and you can undo it with just about anything you have to hand.
I've asked Si if he can get any O-rings or washers to use it for this instead of the rad cap it's designed for. As soon as he does I'm going to replace both of mine.
I'm going to save the old plastic ones though - if I ever meet the Land Rover engineer who specified plastic caps in the diff filler holes, I'll be sure to stick them somewhere appropriate.