I was looking for an air tool rack. The average price I was seeing was between $20 - $30. I thought, I can make one of those & for a lot less than they were charging. Of course, I made it at TechShop. First thing I did was go to a local metal supply store. They have a section they call the drop zone. If they have a 4' piece of stock & a customer comes in wanting a 3.5' piece, they cut the part for the customer & put the rest in the drop zone. The remnants found here are sold by weight. The total cost for this project including screws was less than $3. Now you could do this with a piece of sheet metal & bend it with a brake but then you have to worry about it being strong enough to hold what you want to hang from it. I eventually choose this design based on the scrap metal I found.
The most important thing at this point is to get the slots right. The point on the fitting that will slot into the rack is 0.33". You want to use an end mill that is slightly larger than that but just barely so the fitting doesn't fall out. The spacing between the slots is determined by how many tools you want to hang & how big they are.
I choose to start by laying the plate flat & milling the slots as you see on the picture here. I did this because I wanted the back of the slots to be round & I was using a square end mill.
I then turned the plate vertical & finished out the slots.
I then cut out smaller pieces to make the vertical mounts.
After these were cut out & carefully measured out & lined up the holes then tapped them.
Assemble the parts, screw them to the bottom of a shelf & viola!