- you can measure the with of the threads, should be something like 2-3mm m2, or m3
- the other number is threads per inch or whatever the metric conversion is... you're probably close with 32. doesn't quite look like 40.... 40 looks a little finer than that.
- then you have the length as the other measurement.
so, 4-40 6mm would be 4mm threaded shaft, 40threads, 6mm long
take the screw to the hardware store and match the threads to one that's labeled. like this. (these are coarse deck screws but you get the idea... match the threads)
once you get the specifics, you could even order form amazon.
...they may have a thread gauge at the hardware store to find the thread count (in with the machine screws)