Unless you’ve learned this in school, it’s likely that you know what this thing is used for but don’t know what it’s called.
These things are called cabin hook latches: protecting Filipino homes since the 19th Century, as one online meme pronounces with pride.
These latches trace their history on ships, where adjacent doors would be prevented from swinging around as the vessels bounce around waves in the open sea. With the advent of private property and privacy, the latches found some newfound (and land-based) use, as gate and door locks, among others.
These latches are mechanical fasteners that join two or more objects or surfaces while allowing for their regular separation. The cabin hook latch comprises three major parts: the hook bar, the ring, and the eye screw. These are both fixed with screws or nailed to door jambs or woodworks or walls. The cabin hook latch system will only work if these are on the same level.
Cabin hook latches are usually found on doors, lightweight gates, cupboards, and, well, cabins.
References:
Porter, Brian; Christopher Tooke (2007). Carpentry and Joinery 3. Butterworth-Heinemann. p. 200. ISBN 978-0-7506-6505-6.
interiordezine.com Archived 2008-10-15 at the Wayback Machine