Wobbly brass door knobs

[Saltyandvinegar]

Moved into an old house. Door knobs need tightening. Some look like they are missing a tiny screw in the side any idea what type to order?

Can you take out one of the screws and have a look?

You can unscrew the grub screw and measure it to try and find replacements. In the meantime you could turn the spindle and knob around so the screw goes in from the top and will be less likely to fall out, or wrap a tiny bit of PTFE tape around the thread to stop it loosening.
Play around swapping knobs/screws to make sure if the knob and spindle fall out, you will not be locked in a room (if that makes sense).

grub screw. That was the word I needed. Thank you x

the grub screw holds the knob tightly to its spindle, but if the spindle is a bit long, it will still rattle. sometimes the other end of the spindle has holes at different intervals or a scvrew thread so you can do fine adjustment.

many of these knobs are very old and the screw is likely to be some old non-metric size. I once spent weeks tracking down threads for some old locks.

you'll need to measure it very very very accurately and look up tables of screw sizes. if it measures an exact number of eighths or sixteenths of an inch it might be BSW.

Ordered a mixed bag off Amazon. Winging it and hoping for the best.

If none of them fit try taking the knobs to a local garage and asking them if they can tap a new thread for a known size grub screw

you ordered new screws without measuring the old ones?