Wood 2x4 works well
Step 1: CUT UP WOOD
4.5-6" any bigger might not look so good any smaller might be a square.
You can use a chop saw or a saw
Tech Shop has one.
Step 2: Make Your Holes
Drill as deep as you can. Deeper is better
You should clamp your work when drilling deep.
Step 3: Sand the Rough Edges
Step 4: Special Step
If you want to give them some flair then lets take them to the laser were you can customize them
Tech Shop has Laser they can help.