Towards the end of the last century I treated myself to a Manfrotto tripod and pan head. Not a super model, the basic 190. Anyhow one of the screws used to clamp an extended leg in place went missing. Quick fix was an M6 hex head screw and a knurled knob I made myself. Now the thing is the original screw was twin start to speed up locking, so my replacement always needed more turns. Now I have live with this for 20 odd years, but last time for some reason noticed it, probably because that leg collapsed not being tight enough so i decided to go online to see what I could find.
Onto Manfrotto site, using model number a nice exploded diagram of tripod appears and their is the screw part number and all. Clicked on it and found I could order it. Did so, paying with PayPal and with one working day between placing order it duly arrived in the post. Knob shape is slightly different but works fine. Not bad service for a 30 year old tripod.