Ever see the symbols on the side of your AR-15 upper receiver above the forward assist and wonder what they meant? The mark corresponds to which company made the raw aluminum forging that later became the upper receiver.

The upper receiver forgings are all essentially the same, they simply come from different forging houses. The quality of the upper receiver ultimately comes from the manufacturer that CNC machines the raw forging into the upper. The company that applies the anodizing is then responsible for how well the finish of the upper becomes.

AR-15 Upper Receiver Forge Markings:
A (Splintered) = Anchor Harvey Aluminum
AF = Alcoa Forge
C AF = Colt Alco Forge
C MB = Colt / Mueller Brass
Cardinal (Stylized) = Cardinal Forge
CH = Colt Harvey Aluminum
Circle/Crosshairs w/ “AR” = ArmaLite
CK = Colt / Kaiser Aluminum
CM = Colt / Martin Marietta
D (Stylized) = Diemaco
DK = Diemaco / Kaiser Aluminum
E = Emco
EK = EMCO / Kaiser
E MB = EMCO / Mueller Brass
F Keyhole = FNMI / Cerro Forge
FA = FNMI / Anchor Harvey
FK = FNMI / Kaiser Aluminum
FM = FN/Martin Marietta
FMB = FNMI / Mueller Brass
Keyhole = Cerro Forge
L = Lewis Machine & Tool
LK = LAR / Kaiser Aluminum
LM = LAR / Martin Marietta
M (Under Diamond) = Mueller Industries
PA = Capco / Anchor Harvey
PM = Capco / Martin Marietta
Square = Brass Aluminum Forging Enterprises

The two most popular symbols you will see on AR uppers are the ‘Keyhole’ (Cerro Forge) and the ‘Square’ (Brass Aluminum Forging Enterprises), but you will see more if you keep your eyes open.