The Forged F-height Front Sight Block (FSB) is a mil-spec, military-grade component designed for flat-top AR rifles such as the M4 and M16A4, ensuring proper sight alignment with detachable rear sights or optics. This F-height FSB is slightly taller than the standard height version, making it crucial for achieving accurate co-witnessing on flat-top upper receivers. However, it's important to note that while this is an F-height sight block, it may or may not be marked with the "F," as it is sourced from multiple military contractors and can vary in marking. The story is that once upon a time, when the military was changing from A1 and A2 carry handle upper receivers to the A3 and M4 flat top receivers, the height of the rear sight changed, ever so slightly, and when the FSB was installed on a 20" barrel, that change required an ever so slight increase in the height of the front sight, up by only 0.040", and the new "F marked" FSB was born.
Story goes that the "F" was for flat-top. Who knows, it could have been for new f***er, but so that the Army and Marine armorers could tell the difference, an F was stamped on the left side of the FSB. Fast-forward to 20+ years of only manufacturing flat-top upper receivers, and more and more manufacturers are skipping that step, thinking, who the f**k every buys a carry handle upper. So, the FSB you purchase may or may not be marked, so it is now called "F-height."
Manufactured from 4100 series forged steel and finished with a phosphate coating, this FSB is built to military standards, providing rugged durability in any conditions. It fits barrels with a .750-inch gas journal, and does not include a front sight post, pinholes, or sling loop. This is a basic building block to a quality AR / M4 / M16 build, but installation will require a gunsmith to drill and taper-pin it into place, ensuring proper alignment.
Important Note: This front sight block is not pre-drilled for taper pins and requires installation by a qualified gunsmith. Since the FSB must be drilled and pinned into place, it is critical to ensure proper alignment and fit during installation, particularly when working with a virgin barrel that has not been pre-drilled for taper pins.
This F-height FSB is perfect for anyone seeking to replicate military-correct rifles or enhance the accuracy and reliability of their flat-top AR-style platforms, ensuring proper sight height alignment with modern rear sights or optics. This generic F-height FSB is produced by various military contractors and provides the exact specifications needed for modern flat-top AR builds. Whether you're constructing a military-correct clone or upgrading a tactical carbine, this forged, phosphated FSB ensures reliable performance and proper sight alignment. Its robust construction makes it ideal for demanding use, while offering the flexibility for customization based on your specific build requirements.
Charlie's sources these forged F-height FSBs from a number of leading manufacturers, like CMMG, Schmid Tools, Rock River Arms, Stag Arms, etc., and the quality standards are all the same, built for military rifles, and shipped to manufacturers like Colt and FN. The manufacturer really is a matter of sourcing and which has this product in stock from month to month. You would never know one manufacturer from another. It is a quality utility part, and not a trigger or BCG.
