While I was at the range the other day, a European gentleman came over to talk to me about my carbine and for some reason he took an interest in my front sight post. It’s a stock front sight post (fixed) on my ArmaLite upper. I had a little difficulty understanding him but he said something about mine having “4” and his own AR15 having “5” and he had some tool to adjust his. What was he talking about?
He is probably referring to the difference between A1 and A2 front sight post adjustment bases. A1 front sight posts have 5 adjustment notches, A2 posts have 4.
I think Steel Weasel hit the nail on the head. The A2 has four because it’s a square front sight post where the A1 has 5, since it’s round it doesn’t matter how many stops it has on it.