The Door Chain: A Slide in a Groove, and a Key for the Outside

"The object of my invention is to provide simple and convenient means for enabling the ordinary chain-fastening of street and other doors to be secured either from the outer or the inner side of the door, and in such manner that, while it may be released from the inner side in the usual way, the door cannot be opened (beyond the traverse allowed by the chain) except by the use of a proper key". "The chain B is secured at one end to an eye or staple, b, upon the door-frame F', and is provided at its free end with a slide, B', of the ordinary form." The slide-piece A on the door has a groove open "at the end next the lock or opening side of the door". A stop or bolt and a starting-pin, "each of which is movable at right angles to the slide-piece A", sit in a case let into the door: the slide pushes the pin, the pin pushes the bolt into the groove, and a bar moved by the latch-key holds it there. "By this construction a chain-fastening may be secured as readily from the outside as from the inside of the door, and when secured it can be released in the ordinary manner from the inside of the door, but not from the outside, except by the use of a proper key."

Close the door and mark on the frame and the door a line at the height you want, usually just above the lock. Using the notebook, choose where the staple and the slide plate go for the gap you want, then hold the chain in place to check it before drilling. Drill pilot holes and fix the staple into the frame with the longest screws that will reach the stud behind it: the screws, not the chain, are usually what fails when the door is forced. Fix the slide plate on the door. Put the chain on, open the door and measure the gap with a tape.

**Charles Parham** of Philadelphia filed US 188,664 on 6 February 1877; it is dated 20 March 1877. He writes that a chain-fastening combined with a lock and worked from the other side "has been heretofore known and patented", and does not claim that broadly. **Honest limits.** The patent gives no chain length or positions. The door width, positions and chain lengths in the notebook are examples.