I have looked online but have confused myself as to what the numbers mean on the packaging label for screws.

For example (obviously I understand the 'mm' information).:

A) 10-8 x 100mm           <-- Presumably 10 signifies 10G. What does the 8 signify?

B) 10G x 50mm

C) 10G x 65mm TPI 10   <-- I understand TPI means 'Threads per Inch'

What does 10G mean?

One overseas web site (What size is a 10g screw?) says:

A 10 gauge screw is approximately 4.17 mm thick. This is a bit thicker than ⅛ inches, which is 3.175 mm. One of the most common sizes of screws, 10 gauge screws are used in a variety of applications, from light construction to home repair projects.

10 gauge screws are often used for fastening drywall, framing, and plywood, as well as for anchoring outdoor fixtures such as mailboxes and swings. The head of the screw measures at 4.93 mm and the thread diameter can range from 4.5 mm to 4.7 mm.

But this NZ site (Screw-Diameters-Pilot-Holes-230309.pdf) says:

If anyone knows of a good screw chart for New Zealand, a link would be useful.