Use the 3/8" drill bit for wood that is at least 7" long to drill the holes through the 6" long block. This is the most challenging part. Normally, bench press would be perfect for this job, but not all of us have bench press that can drill perpendicularly straight down. I use a drill that have a built-in leveler at the back. It helps me drill holes straight down. If you don't have such a drill, you can use an ordinary drill and a 3" square brace. Place the brace flat on top of the wood, then align your drill bit next to it to guide it straight down. After you drill about 3", you can remove the brace and you should be able to drill straight down without a problem. The drill must go through the 6" block of wood, end to end.