Tanks for the quick response guys. Yeah, I definitely will take a better look at the badger nozzle. So far it's the best candidate. Although I do not think the ballpoint tip is out of the question. If we say the glas vial is appr. 3in, then the tip would be appr. 7/8in. I measured a pen tip I had and it was 5/8in. I'm sure that if I find tips with the knurling at the bottom they will also be longer. I'm just thinking rational here. I mean if the pens exist it is not unlikely they used that solution. (think quantity, price)
Though the cake decoration nozzles look good, and are maybe close enough, they lack the knurling at the bottom plus they have a seam. I don't believe they were used. The part looks like it's in one piece and I'm almost certain that I've seen pen tips like that somewhere.
Below is a quick comparison of a screenshot and the pen tip I had. (the glove is just to match the scale better)