I'm building a roll cage at the mo and was thinking of making this front sticky up bit but I don't no what it's for. Is it to help protect the bonnet if you are upside down.
To my knowledge, it is to prevent damage to the radiator in the event of a rollover (as in so stop it from being crushed and stop you from getting home!)
They are to help stop the car rolling forwards. Icelanders use a version of them to stop the car falling down a crevasse, if you have any where you live