This is a collection of jigs to help drill two holes in exactly the right place to connect two 2x4s. Some are designed for two ends to be connected together, while others connect the end of one to the middle of the other.

The holes have an 1/8" diameter, which is about right for construction screws, but they can also be used as pilot holes for larger drill bits. The photos included are of boards with larger holes drilled for 1/4" hex bolts.