Any one know where i can get parts like this?

http://www.ebay.co.uk/itm/3504964514...9#ht_650wt_952

Only really need the bit that clips onto the ball joint. One of them on our horsebox popped off yesterday when the misses was on the way back from a show. Luckily she was only 30 miles away so i got out to here and managed to cable tie it back on to get her home.
Ideally i'd like to replace all three, The ball are ok as they are steel but the bits thats push onto them are nylon.

They are M6 thread like the on in the link but only really need the clip on bit but don't know what they are called.

Thanks in advance.