A Colt A2 "F" height front sight base — a factory take-off FSB with bayonet lug, taper pins, and an optional sling loop, for A3/M4 flat-top builds.
The A2 "F" height front sight base is the factory Colt FSB for flat-top A3 and M4 upper receivers. When the AR-15 and M16 ran the integrated A2 carry handle, the front sight sat at a fixed standard height. When the flat-top receiver replaced the integrated carry handle, the sight-over-bore relationship changed, and the FSB got slightly taller to bring the front sight into alignment with the new rail-mounted rear sight. Colt marked those taller bases with an "F" on the sight post to distinguish them from the earlier standard-height FSBs. Today, virtually every rifle running an FSB is on a flat-top, so Colt has largely dropped the "F" rollmark as a production step — but the part is the same "F" height FSB whether or not the post carries the letter.
This is a factory Colt take-off — pulled from a new Colt upper receiver group or rifle that was test-fired at the factory and then disassembled. The part is 100% genuine Colt, ships with Colt-installed sight pins, two original taper pins, a bayonet lug, and the sling loop installed unless the "without sling loop" option is selected. Customers most commonly choose "without" when they plan to install a Colt M4A1 side sling swivel inside the A-frame, which only fits if the sling loop is out of the way. The base may show Colt factory oil in the bag — that is intentional and correct.
This is probably the best A2 FSB available on the market, but installation is a gunsmithing job, not a drop-in part. The base is pinned to the barrel with taper pins, which are tapered, not straight — the installer has to ream the barrel's taper-pin holes to match, hold the FSB dead at 12 o'clock to align the gas port with the gas tube hole, and then set the pins to spec.
Critical installation note: this FSB has been removed from a barrel and therefore has taper pin holes already drilled — the barrel it is installed on must be virgin (no existing taper-pin holes). Installing on a barrel with existing holes will not align. The gas port must index correctly to the gas tube, and the pins must sit tight. Have a gunsmith handle it.
We don't normally stock standalone FSBs, but this one came up often enough in builder requests that we set aside a run. If you're finishing a retro A2 or a modern flat-top and want the Colt factory part instead of a mil-spec commercial copy, this is it. Order yours today — we'll get it packed and shipped.
