Done a search, but couldn't conclude on the correct answer.....How do you add them?, and what do you use? :-)

You can use split collars, but beware of the size as on one side of the rack the lock stop needs to go inside the rack on full lock and will really limit travel if it is too big,

Jubilee clips do the job and different widths will give you different restrictions - on the rack just behind the knuckle.

I used an inch of thick walled tube that fitted neatly on the rack, split it then used a jubilee clip to old it together.

OK...cheers chaps, will get on to this.