lock
I saw this recently and wondered:
Why are there two lock cylinders?
How does this work?
Is this how this thing was originally designed?
…and thought someone on this site might have some insights.
The lock was on a closet in a room and building that are generally accessible by the public, which is owned by a civic institution.
You can try a different search phrase as "Thumb Turn Security Latch".
There is a seller on eBay that has new stock available in range of finishes. Here is a picture of the offering.
Considering the price you may just want to consider purchasing new units instead of trying to locate parts for the old ones that are broken.
The trade name for these seems to be: Deltana mortise bolt
You can find those at many web sites including at MyKnobs.com.
Here are some dimensional pictures from a Deltana specification sheet so you can compare to your existing items.
These are usually called "rim locks" in North America and the UK. Maybe different elsewhere.
Best Answer
Well, the ones inside a bank's vault need Their key and Your Key to open Your safe deposit box. For instance.
Designed that way.
Requires two keys to operate. Normally applied where two separate people hold one key each and need to both be present when the lock is opened.
Depending on design, could also be used so that a primary key is used at the start of working hours and then a secondary key will operate the lock, but only during working hours (the primary key would be run around the building and used to lock the primary lock at closing time.)