The CMMG F-Marked Front Sight Base Assembly (brand part no. 55DA338) combines a front sight base with an integrated gas block, built to fit AR-15 barrels with a .750-inch gas journal. Machined from steel and finished in black matte, it carries the taller F marking that pairs correctly with a flat-top upper’s higher sight plane, so a folding or fixed rear sight lines up properly at eye level. The assembly ships complete with the front sight post and sling loop already installed, giving builders a ready-to-pin unit rather than a bare block. Because it doubles as the barrel’s gas block, it’s a common early step in any AR-15 upper build using a rifle-length or mid-length gas system. Taper pins are not included and must be sourced separately to complete installation.

Key Specifications

• Carries the F marking for correct sight height on flat-top uppers.
• Fits barrels with a .750-inch gas journal.
• Functions as a combined front sight base and gas block.
• Includes the front sight post pre-installed.
• Includes a sling loop pre-installed.
• Machined from steel for durability under heat and pressure.
• Finished in black matte to match most AR-15 builds.
• Built as a genuine AR-15 accessory part.
• Does not include taper pins, which must be sourced separately to install.

Frequently Asked Questions

Does this include taper pins? No, the taper pins needed for installation are sold separately.

What gas journal size does it fit? A .750-inch gas journal.

What is the F marking for? It signals the correct sight height match on flat-top AR-15 uppers running a folding or fixed rear sight.

Buy the CMMG F-Marked Front Sight Base Assembly – AR-15, .750 Gas Journal

Get your flat-top AR-15 build sighted in correctly from the start. Order the CMMG front sight base from our gun sights selection at our Lubbock, Texas gun shop for fast, direct shipping.