Reddit reviews Prime-Line Products E 2281 Passage Door Latch, 9/32 in. & 5/16 in. Square Drive, Steel, Brass Finish
We found 1 Reddit comments about Prime-Line Products E 2281 Passage Door Latch, 9/32 in. & 5/16 in. Square Drive, Steel, Brass Finish. Here are the top ones, ranked by their Reddit score.
This door latch is used indoors with old style passage lock sets2-3/8 in. backset, accepts 9/32 in. max. square spindleBrass plated finishConstructed of steel and diecast components
Without the context of the rest of the lock, it's hard to say. Based on what's there, I'd say what we're seeing in the picture is probably either the override for a privacy function mortise lock (smaller square hole near top), or (less likely) the knob spindle hole of a mortise or crossbored lockset. Lack of screw holes around the hole make me strongly suspect the former. Either way, it's something meant to simply be turned with an appropriate sized square tool.