When I bought my bow I got a free dozen black mambas (I'm sure I paid for them) and I've designated them as hunting arrows. I took them to the my local bow shop and he was baffled. They have a inner rod and calls for a stainless steel collar? I/we figured out the inner rod deal (just cut it to length and subtract the length of the insert), but I/nor he is sure what the collar's are. I don't have the above mentioned collars. He suggested that it might be collar's under the nock, but the nocks fit perfect? Any help would be great.