I have a set of A.R.M.S. flip-up polymer backup sights, nomenclature 71L-R and 71L-F. The front sight should not be mounted on a gas block since it is polymer. The rear sight impacts the scope on my AR when deployed, and I don't have a tip-off mount for the scope. I have acquired a pair or offset sights that work just fine, so these are surplus. I paid over $70 for the pair. Yours for $50. Portland area, or ship for $5. My blunder is your opportunity. Don't let someone else take these.