Mighty
It is a little harder if you do not have the proper tools, depending on the materials you will be working with, if you use solid copper and zinc rods you will need to cut carefully with a fine metal saw, file away all the sharp corners, sand and polish the rods properly. Once this is done, it’s not too difficult to insert a 3/8” rod into the 1/4” opening of a rubber tube, you may have to use a needle nose plier to stretch the opening, but strong narrow fingers may do it.
Now if you are going to use 3/8” hollow copper tubing, then you may want to use a proper tube cutter tool similar to the ones used by your friendly plummer, cutting with a hacksaw may distort the shape and may not hold too well inside the rubber tube. Please go to Tom Hubbard’s Penis Workshop site link at the bottom of this screen for more detailed instruction. Once assembled, it is a wonderful piece of art.
If you don’t want to do it yourself, I can put one together for you. I have already made a few for my own use and experimentation. I have all the materials required to make a few more ballzingers. If you are interested, send me a PM.