The instructions used were those from Pete's home made violin tools FAQ from website http://home.att.net/~PeteSchug/homemade.html. The timber used was 1" thick doweling cut into pieces approx.1 1/8" long, then each piece was end faced in a lathe and lined drilled with a 1/4" drill to a finished length of 1" each. The bolts are standard 4 1/2" x 1/4" carriage bolts, the washers are full size but could be of a smaller diameter if desired and the middle faces are lined with good quality automotive cork. I made a total of 36 which is sufficient for violin and viola work.
Things to note:- 1" diam. is the maximum I would recommend, as when using this size at the centre bout they can impinge on the arching and cause marking, particularly if the edges are left sharp and thin or no lining is used.
Also, the outer edges of the wings on the wing nuts need grinding or filing back slightly, otherwise if the clamps are touching they can touch the adjoining ones when being tightened.
Whilst I had the use of a lathe for very accurate finishing, as long as a little care is taken during the cutting and drilling the only tools required are a drill (preferably a drill press), grinder or file, suitable glue and the raw materials, as ultra precision is not needed for usable clamps.