The threads of a screw used to fasten two pieces of wood are pitched at an angle. How does this increase the static friction force?

Question

a) by increasing the surface area between the screw surface and the wood

b) by increasing the ease of inserting the screw into the wood

c) by increasing the coefficient of static friction between the screw and the wood

d) by increasing the normal force exerted by the wood on the screw thread

Answer 1

d) by increasing the normal force exerted by the wood on the screw thread