From Madbull, these are fully licensed Daniel Defense style Aluminium outer barrels. Tough, light and high quality; Madbull makes some of the best outer barrels around and they offer them in a broad variety of lengths. A standard M16 has a 20 inch barrel while the standard M4A1 has a 14.5 inch barrel but the beauty of the M16 family is their ability to modify the length with a lot more options then that.
The 14.5 inch barrel is standard M4A1 carbine length so while it may lack the exotic personalization of a non standard length it will certainly be easier to shop for inner barrels. You can swap out to a Daniel Defense barrel without having to affect your internal setup or practical performance at all.
Madbull makes a variety of 14.5 inch outer barrels so do be sure to poke around to see exactly which design you like the most.
Note: Item comes in 14mm CCW threading