Repairing balance control on a Nikko NR-750 Receiver

[thevenetian]

Got this receiver from craigslist for $20 untested and figured I'd take the risk. Got it home and it seems to be working, except that the knob for the balance is loose so when you turn it, its not actually turning the unit inside.

Removed the top of the unit and can see that the screw that holds the plastic knob to the shaft is missing.

Looking for assistance on where I could find that size of screw, or how to even measure it so I can go online and hunt it down. Perhaps there is a set of a certain sized screws I can get and assume it will be included.

See photos.

[fzabkar]

If it helps, it's called a "grub screw".

[drknob]

https://www.amazon.com/Hilitchi-260pcs-Socket-Assortment-Plastic/dp/B014OMFU1I/ref=sr_1_6?ie=UTF8&qid=1546439821&sr=8-6&keywords=grub+screw

[coromonadalix]

Or called "set screws",  flat screw driver, or hex screw with some allen keys

Not sure of the dimensions, we use at my job metric m2 or m2.5 screws in similar shafts / knobs ...