The "Base Board" is the 48" 2x4 that doesn't have a pulley bolted to it. It gets a hinge in this step. We traced the hinge to make sure it didn't move while we bolted it on. Then we drilled pilot holes for the 1/4" bolts. A washer goes under each bolt head. The 1/4 x 1.5" lag bolts we used to hold the hing on. If you use a different style of hinge you may have to use flat head screws instead of hex heads like we used.