A selection of my parallels.
I have some round sets of 4 all of the same height about 8mm tall and 20mm tall usefull when holding castings etc. A pair of 1"x1/2" x 9" long a pair of 12mm x 25mm x 150mm long which do most of my heavy work. I have a set of adjustable Starrett parrallel which are useful to measure steps and slots as well as adjusting to support a job. I also have two pair of thin parallels so i can drill a job without hitting the parallels, these are 1mm x 20mm x 75mm long and 1.5mm x 25mm x 75mm long. I also hsve a few other general purpose pairs of parallels of various thicknesses that I have collected over the years. These are all hardened and ground whilst at work for various jobs. The thin pairs of parallels have a tendency to tip so I put a light 12mm diamiter spring between them when in use. You can't have to many parallels.
David