On Jan 8, 4:57*am, "Steve B" wrote:
You mount it on the top of a door, vertical, pin pointing up, chain hanging
down. *It has a chain hanging down with a ring. *The upper end of the chain
is attached to a slider bolt. *The upper end of the bolt is shaped like the
part of a door closure that runs along, then into the pin hole to hold the
door shut. *Usually used on the second door of a set of two to hold the top
shut when there is not a big need to have it shut really tight or secure.
First door has passage lock or exterior door knob lock on it. *Available in
large sizes, too.

What are they called?

Steve

(Door) security chain.
http://en.wikipedia.org/wiki/Security_chain