Gee Fred, the manual confirms what you posted alright. I pulled one of my screws and it is a #8x3/4. I have had them in for 40 years and never had a visor fall off and hit me in the head! I will try a #10 and see how easy it screws in.The pictured and measured metal screw came right out of my pickup visor today so i could remove the roached headliner trim.
GROUP 31-03C - SUN VISORS
Part No. GM-162474 Screw, oval hd., No. 10 x 3/4”