I've had it so long I forget who made it. I cant be 100% aout the constriction on it I think it was .640 but I do remember that when I measured it I looked up the bore size of a 16 ga. and it was'nt to far from it.
I thought it was a Hastings, but it looks more like a Nu-Line Extra Long Tube.

It says 5X on it ( meaning 5 times an extra full. )