The image is of what we are screwing hot & shade house together with. We call the screws 4 inch batten screws with a inverted hex head. The drill has a hex head driver in it. This is the easiest way to put screws into timber. A pilot hole that is a smaller diameter, drill bit is used to help the screw going into the timber without splitting the timber. There is an image of this below!
Our posts are at 4 foot centers with 4 inch x 3 inch x 8 foot high with 2 foot into the ground. We have post that are 3 inch x 11/2 inch in the middle of the larger posts.
All other timber is 3 inch x 11/2 inch. All timber is treated for termites & rot proof. The timber type is a heavy pine with small knots that has no structural rating.