G5 Meta nocks
I think this is what you have.
It is hard to tell from your pic. This is what i could find that "looks" close. Let me know if it is. There is also a nock made by bohning that is simular.
They're not the G5 Meta nocks - they're a discontinued CX nock. I can't remember the name - I have an older CX catalog at work, and if I remember, I'll post on Monday with the info.
I'm told that these are called CX "Express" nocks. As I said, discontinued a few years ago, but you might still be able to find some. They have a bigger throat (looser fit on the string) than the current TCX nocks.