Deltana SDML334 Storm Door Latch, Square, Mortise Lock

Mortise. It installs into a pocket cut in the edge of the door stile rather than screwing onto the face, which is why the door thickness range of 7/8 to 1-3/8 inch and the 1-1/2 inch backset both have to check out before you buy. If your storm door has no mortise pocket and you do not want to cut one, a surface mounted storm door latch is the easier retrofit. If the pocket is already there from the original latch, the mortise version gives you the cleaner face with the brass escutcheon covering the prep.

Backset is 1-1/2 inches, measured from the door edge to the center of the spindle, with a 3-3/4 inch face plate. Storm door manufacturers are not consistent on backset, so measure the existing pocket before you order: if your old latch centers at 1-1/2 inches and the mortise pocket accepts a 3-3/4 inch face, this swaps straight in. A 2-3/8 inch backset, the common bored-door figure, is too deep for this latch.

Nine finishes: PVD Polished Brass, Polished Brass, Antique Brass, Oil Rubbed Bronze, Brushed Nickel, Antique Nickel, Polished Chrome, Brushed Chrome, and Paint Black. Finish is the only thing you choose on this latch, everything else is fixed, so pick the one that matches the entry door behind it. PVD Polished Brass and plain Polished Brass look similar on a sample board but the PVD version is the one to use where the storm door takes direct sun and rain.

Mechanical only, no electronic or electrified option, and it is specified for residential use. Treat it as the outer layer on a storm or screen door in front of a real entry lock, not as the primary security on the opening. Landlords furnishing units get the benefit of a solid brass latch that stands up to daily use, but the keyed entry lock behind it is still what secures the unit.

Model SDML334 is the square version, meaning square escutcheon plates and a squared face rather than a radiused one. The mechanics are the same class of part: 1-1/2 inch backset, 3-3/4 inch face, reversible, for 7/8 to 1-3/8 inch doors. Choose square when the storm door and the entry hardware behind it have squared trim; the shape is the differentiator, not the fit.