Deltana MB175 Mortise Bolt, 1-3/4" Backset, Solid Brass

That is exactly what the MB175 is built for. It's a mortise bolt, so the body pockets into the edge of the door and the face plate sits flush, which keeps a thin screen door or cabinet stile looking clean. Deltana rates it for residential use, not commercial openings, and the 7/16 inch bolt throw tells you the rest: it's a secondary security and hold-shut bolt, not a primary entry lock. On an exterior entry door you still want a deadbolt doing the real work.

Backset is 1-3/4 inches, measured from the door edge to the center of the turn. That's the number to check first, because the bolt body mortises into the door edge and the turn has to clear whatever is beside it, a glass stop, a panel edge, or a screen frame member. On a narrow stile you need at least 1-3/4 inches of face material past the edge for the turn to sit where it belongs.

Bolt throw is 7/16 inch, so the pocket in the jamb or the mating door only needs to take a shade over that. Shallow prep is one of the reasons this style suits screen doors and cabinet frames where there isn't much material to drill into. It also means the MB175 will not span a sloppy gap; if your door-to-jamb reveal is running wide, 7/16 inch of projection leaves very little engagement.

Deltana lists the MB175 as residential hardware. For a commercial corridor pair or anything on a fire-rated opening, specify a commercial flush bolt built for that duty rather than this bolt. On apartments, houses, screen doors, cabinets, and interior pairs, it's in its element.

A mortise bolt like the MB175 buries the whole body inside the door edge and shows only the face plate and turn, so nothing protrudes into the opening and there's no barrel running up the face of the door. The trade-off is prep: you have to route a pocket in the edge, and the door needs enough meat to take it at a 1-3/4 inch backset. A surface bolt screws straight onto the face with no routing, which is the faster retrofit but leaves visible hardware. If the look matters, or the door swings against something the bolt would foul, mortise is the one to specify.

Nine finishes, which is what makes it easy to match to the rest of the door hardware: polished brass, antique brass, PVD polished brass, oil rubbed bronze, brushed nickel, antique nickel, polished chrome, brushed chrome, and paint black. The PVD polished brass is the one to specify where the bolt sees weather or frequent handling, since PVD is a plated coating over the brass rather than a lacquer. All nine are the same MB175 body, so a property manager standardizing across a building can order one bolt in whatever finish each unit already carries.

Solid brass, both the material and the substrate on the spec, not a plated pot metal core. That matters on a screen door or a coastal exterior application where a plated zinc bolt corrodes and seizes inside the mortise pocket. Brass also machines and wears well enough that the bolt keeps sliding freely after years of use.

Yes, that's a standard use for it. The MB175 mortises into the edge of the inactive leaf and throws its 7/16 inch bolt into the head or the sill, holding that leaf fixed so the active leaf has something to latch against. Deltana lists it as residential hardware, so it suits a house or apartment pair rather than a commercial opening that needs a fire-rated flush bolt.

The MB175 is a mortise bolt, not a lock cylinder, so it operates from one side only and takes no key or keyway. Nothing to key alike, nothing to master. If you need keyed control on that door, the mortise bolt is the wrong part and you want a keyed deadbolt or rim lock instead; the bolt is for holding a leaf or a light door shut from the inside.

The MB175 is sold each, one bolt per unit, and the price shown is per bolt. On a pair of doors where you're bolting the inactive leaf top and bottom, that's two units per opening.