YHM Yankee Hill 9680 A1 or A2 Flip Up Rear Sight BUIS
Features of this sight include: a rugged but lightweight design with a steel base, a quick release thumb screw, and aluminum stem. Locks in the deployed position with ease and won't fold down without depressing the locking detent. Don't consider a BUIS (Back Up Iron Sight) without this. When folded it measures only .840 inches from the highest point down to the top of the upper receiver. It has a 1/2 M.O.A. windage adjustment and comes with a standard rear peep aperture. Mounts to any Picatinny rail. Designed to co-witness with the standard M16-M4 front sight and all of our front sights.
YHM-9680-A1 is a special design that has all the same features as our YHM-9680 model but features an A1 style windage wheel with a 1/2 M.O.A. windage adjustment. It prevents accidental adjustment of the sight. To adjust, simply depress the plunger with a bullet tip and rotate the wheel.
What is co-witness?
A: Co-Witness is the ability of your irons to look through your optic (1x - not magnified) - so they both shoot on the same trajectory. There are two kinds - absolute (both the dot and irons are on the same plan), and offset (where the irons are usually in the lower 1/3 of the optics display...uses a riser). With co-witnessed sights you can verify the zero of the optic by looking through the irons (the dot should sit on top of the front sight). However, normally you look over the irons and just use the optic (trust me, you won't notice the iron sights); should the batteries fail your head comes down a fraction of an inch and you're using the iron sights (looking through the now-dead optic).
With a MEPROLIGHT tritium front sight and this rear, you can have 3 dot green front & green rear night sights for M16/AR15. Green lamps are warranted for 5 years from the date of purchase. MEPROLIGHT 3 Dot night sight sets are designed and assembled with the optimum combination of strength and safety. Machined from steel rather than cast, their strength is unsurpassed. MEPROLIGHT night sights are the brightest, strongest and safest.