The washer, which has been used for the bolt head to slip on now becomes the limiter for the T-nut. Do not tighten the bolt too much as you may cause damage to the T-nut by pulling it too tightly against the washer. Once the T-nut is in place, back out the bolt and remove it and the washer. Now, start at step 5 and go backwards to restore the theremin to its playable condition. There are basically two methods to do this.
Some camcorders have a removeable piece which can be attached to the theremin.
The piece, with the theremin attached, is then replaced and tightened. Some camcorders, such as the one I was lucky enough to find, has a flat surface with the mounting screw in its center. On these place the hole with the T-nut over the mounting screw and tighten the screw. The camcorder tripod I found was manufactured by the Star-D Mfg. Co., Inc. in Jersey City, NJ, and the model is the Continental . I do not know if the company is still in business, and, if they are, are whether or not they are still manufacturing this model tripod.