Nationals have a couple holes bored into the frame behind the left and right side tops of the typebars where the device hooks into. From there the device runs down the sides of the machine where it fit snuggly between the frame and ribbon spools so it didn't swing freely or pop out even if the machine is upside down. The curved part of the device presses against the typebars just above the slugs. It's so brilliant in its simplicity.
National Typewriter Typebar Lock
1889 - 1903
National Typewriter Co.
Philadelphia, Pennsylvania, US
Here's one that was way ahead of its time: a typebar lock. Some of us have seen these if we were fortunate enough to find a modern portable typewriter with all of its original packing materials. Included would have been a plastic, crescent-shaped typebar lock, which was fairly common, but the one on this page is the earliest known example of such a device. It was produced specifically for the curves of the National typewriter.