Here is the basic form that students make then use when they build a rod  at my house. It means that they will have a form to use if they want to build additional rods. One friend built 30 rods on his form before he bought a steel form.

Here is a fuzzy view of the end that shows the grooves that are cut into the top and bottom just like a steel form except not milling machines are needed.

Here is a picture of the adjusting cap screws. On pushes to open the forms and the other pulls them together. Only the only pulling them together goes all the way through. I use simple ¼ cap screws with standard ¼ X 20 threads. They are larger and I think are better in the wood.

Here you see the adjusting screws from the side with the pin in the middle that the forms slide on. I use a reamer to make the pin hole large enough to allow them to slide.

Here is the simple cutter for the grooves. It holds the 60 degree lathe tool upright with 0.200 of an inch width sticking through.

Here is the top view of the holder – super simple.