In the past when I picked up an ordinary woodscrew, I used to look at the head diameter and could usually guess what "number" it was. If I had to measure it then the head diameter in millimetres seemed to give me that "number" value.
Now I want to get some replacment screws by ordering online but it's all metric and seems a bit of a muddle to me.
Is the head size of a woodscrew still a good guide to the shaft diameter? The illustrations I've seen suggest it might not be. If I can't use the head size to determine the shaft diameter then what measurements should I use?
In the end I want to order some (metric sized) woodscrews similar to the ones I have (the older ones are probably imperial). How can I do this? I can take accurate measurements ofmy woodscrews using calipers but how do I translate that into what I can order?