Its just a bit of 10mm tube about 6" long with a flared end and a slight bend about 60mm from flare hope this is right and helps but don't worry if I'm wrong someone will let us know :lol: Frankie.
I tried to make one once after I lost it (I suspect my brothers dog..) - not worth the bother, mine didn't sit right. Can be bought almost anywhere VWH, JK, Coolair) for less than a fiver.