The subject came up about Manual Flush Bolts. Flush Bolts are use on the inactive leaf of a pair of doors. Their function is to keep the inactive leaf secure. Some are UL rated (there are provisions in some jurisdictions for manual flush bolt on pairs of fire rated doors). The word "Manual" means that a person has to release the lever and then reverse the process afterword. Normally there are 2 per door - Top & Bottom. But there are 5 different types - just by Rockwood, not to mention at least 3 other types by other companies.

Rockwood UL Listing 13S2
The Flush Bolt most used is similar to Rockwood 555, this is an ANSI flush bolt prep - which means it's cutout is 1" wide x 6 3/4" length. It is the standard manual flush bolt in the commercial industry for Hollow Metal Doors. Rod length can be ordered as 12" (standard), 24" or 36" - these dimensions are from the top and/or bottom of the door to the centerline of the flush bolt prep.  UL listed up to 4/0 x 10/0 door. Available in many finishes including  US3, US4, US10, US10B, US26 & US26D

Rockwood 555 Flush Bolt
Other Brands: ABH # 1855S, Burns Mfg # 590, Don-Jo # 1555, Door Controls # 780F, Hager # 282D, Ives # FB458, & Timco # 3917.

Another Manual Flush Bolt is similar to Rockwood 550. This is similar to the 555 above but it is 1 1/4" wide. Not an ANSI prep. It has a UL listing for doors up to 4/0 x 10/0. This flush bolt is not common. Because of the 1 1/4" width this would be good for retrofit on old projects, or doors thicker than 1-3/4". This is also available in 6 finishes - US3, US4, US10, US10B, US26 & US26D.

Other Brands: Ives # FB457, & Timco # 3915

Rockwood Flush Bolt 557
Rockwood 557 Flush Bolt
The next most common Manual Flush Bolt after the 555 is the Corner Flush Bolt similar to Rockwood 557 This bolt is used only on Wood Doors. Used at the top & the bottom of the inactive leaf to secure the door. This is UL rated up to 4/0 x 10/0 doors. Again there are provisions for manual flush bolts on fire rated doors.

Other Brands: ABH # 1857S, Burns Mfg 591, Don-Jo # 1557, Door Controls # 790F, Hager # 281D, Ives # FB358, & Trimco # 3913

If you use any manual flush bolt on a fire rated door, make sure with AHJ if it is ok to be used. Most the time the answer will be no - it must be an automatic, self latching bolt.  (AHJ = Authority Having Jurisdiction)

Adams Rite 1870HM Flush Bolt

The last Flush bolt I'd like to show you is from Adams Rite, part number 1870HM this is not a normal flush bot, and Not ANSI prep. But is is available for commercial use, it is lockable and unlockable with a key using a mortise cylinder. They have one model for Aluminum doors (#1870) and another for Wood doors (#1877) The key could be tied in with a master key system.