Step 1: Parts
I used 1/2" PVC because I already had some. I purchased half-inch T's and flat top plugs. You can use a wooden dowel or PVC pipe. I just used short screws for the plugs that I already had and some bolts and nuts as well. I cut the pipe about 12.5 inches per side but probably could go longer.
Step 2: Drill Holes
I drilled a small starter hole in the top of each plug. I drilled a hole as big as my bolt through the plug and the T while they are pushed together. The reason you do this instead of gluing the plug to the T is because you have to be able to get to the screw in case it loosens up from the shelf bottom.
Step 3: Mount the Flat Top Plug First
Pre-drill a starter hole in the bottom of the shelf. Then just screw the plug to the shelf as tightly as possible.
Step 4: Assemble the T
Assemble the T to the plug and bolt them together. This photo shows how it should look after it's mounted.
Step 5: Decorate or Paint the Arms Then Insert
My daughter decorated the arms with her duct tape. We painted another one. If you're going to hang jewelry you may want some of that gray pipe phone to keep it in place.
I just pushed the pipe into the T but you could glue them in or even bolt them in.