Not sure what anti-ND is but in the context of the image that would be a "auto sear". Think of it as a "full auto button" for a glock. I have never seen one in person but it seems like a particular group of the population ends up being arrested with them in their possession. [edit] I am a moron. ND = negligent discharge (accidental discharge). Its a "dont be a fuckup" device that apparently does not work very well.