A manual flush bolt requires someone to lock, and unlock it manually.
These are commonly seen on commercial double doors, such as in a school or a hospital where larger entrances are often needed to accommodate varying traffic flows. Security Surface Extruded Aluminum Flush Bolt in Satin Chrome Finish Trans-Atlantic flush bolts are for commercial spaces or heavily used residential spaces, and are perfect for locking double doors because of the way it lays flush with the side of it's door.