That pretty well says it. These sights carry the A.R.M.S. label and are designated #71L-R and #71L-F. I had these on my AR but they interfered with my scope when flipped up and the scope is not on a tip-off mount, so they just don't work for me. I have replaced them with off-set sights which work just fine. I fired about 120 rounds with these on the AR, and sighted them in before I mounted the scope, but they are basically brand new. You would not want to mount the front sight on a gas block since they ARE polymer. I paid $70 for the pair, yours for $50. Prefer FTF in the west Portland area, but I can mail them for an additional $5. Good deal if you need flip-up sights.