If you have an older vintage doorknob like this on one of your doors and it comes loose like they do a lot of times, it’s an easy fix. There’s a metal connecting rod that binds these two handles together — runs through the door — that actually has threads on it. There’s a little set screw on the handle that holds this in place once you’ve threaded it all the way to the door.
So to tighten this up, you wanna make sure that that’s nice and loose, and just thread it right back on the rose plate. Once it’s nice and tight, you can go ahead and reset that screw, but make sure not to over-tighten this. If you over-tighten it, you can bind up the latching mechanism and the door won’t close right.
Once you have the door handle threaded back on, you can tighten that set screw back down on the handle, and it will hold it in place so it won’t come loose again.
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