GMT stands for Greenwich Mean Time, later came UTC universal time.
Of use mostly in avaiation, pilots as well as frequent flyers.
Basically for keeping track of your local time zone in respect with Greenwhich or UTC time.
To read time in two different time zone.
That is all I know, I swear
Unless you have another watch you can steal them from, it will be hard to say that they are "screw x".
You should be able to get those from a normal fastener supplier though. You just need to know the thread pitch, diameter, and length of the screws. You can measure the thread pitch with one of these: https://en.wikipedia.org/wiki/Thread_pitch_gauge
Note that metric and imperial systems measure screws differently of course, so if you're having trouble getting something that is exactly right, try using the other system. Googling around should get more details on getting the right measurements.