F marked front sight base

[ripper90]

What does the "F" mark on a front sight base mean? I read in one post here it means "flat top". Is that true?
Ripper90

[epa223]

Essentially. Because flat-tops are made with a bit more metal on top for the rail. In order to try and keep the "carry handle" on a flattop, they had to reduce the space for your fingers to carry it. So, in addition to the "squished" detachable carry handle, they raised the front sight base slightly. This combination allows for a better sight plane. You can use an "F" marked barrel on a fixed carry handle upper but you have to turn the sight post farther into the base. And vise verse, a Flattop upper on a Non"F" marked barrel would require a taller A2 front sight post. There are a few companies that used to sell these taller sight posts years ago when this issue came about.