Although the 3-prong flash suppressor was reputedly somewhat more effective than its successor, the birdcage, it had an annoying tendency to become hung up on vines and such while in the field.
A special armorer's tool, a plate with cutouts for the prongs, was slipped over the open end of the FS to install and remove it.
Unlike the European 4-prong FS units that were its contemporaries (on other rifles), the 3-prong could not easily be used as a wire-cutter.
Although often seen on older weapons, the 3-prong is seldom seen as OEM equipment, and is usually replaced when the weapon is overhauled.