A friend gave me some unused Korkers Predator Spikes, which are "5/16 inch hex spikes, extra hard patented stainless steel, Klaw Kut head for maximum bite". I tried them in the same pattern you see in the picture. Why so few? I followed some forum poster who said less was more when it came to studs in wading boots.
I didn't like the feel of how studs made contact with rocks, compared to felt, though they bit better than rubber. But the Korkers P Spikes pulled out of the LL Bean soles frequently. What you see now are 17 cent each galvanized sheet metal screws, #8, 5/8". I don't know how long they will wear compared to the Korkers studs, but they bite as well, and are holding in more reliably probably because of their fatter (#8) screw part.
You guys know something better? Better rubber? Better studs? Better stud pattern? Having tried it all, sticking with felt?

John