Here is a "basic" on the "more current" screws, there are only 2 diameters/pitches, a big difference between some is the head diameter, and thickness. The P220/P225/P225A1/P230 and P232 all use 5mm diameter with a .8 Threads per mm, the P226/P227(w/inserts)/P228/P229/P239 use a 4mm diameter with a .7 Threads per mm. Even though measurements are given in fractional dimensions on the "display", remember Germany uses the metric system for measurements...
Some of the very early P226 from Germany used a slightly different as shown below. Chart from Top Gun Supply, FAQ
***Edit - 7/3/20 with assistance from member MaverickDMD, it has been found that the early Sig Sauer Grip Screws, ase essentially the same as the Beretta M9/92/96 Grip Screws, at 3MM-.5 coarse pitch***
Some of the very early P226 from Germany used a slightly different as shown below. Chart from Top Gun Supply, FAQ
***Edit - 7/3/20 with assistance from member MaverickDMD, it has been found that the early Sig Sauer Grip Screws, ase essentially the same as the Beretta M9/92/96 Grip Screws, at 3MM-.5 coarse pitch***