Jamey thanks, The larger perforation is .50 cm and the smaller one about .33 but I don't know how to measure width or tapering of the channel itself. How do you do it? With silly putty? I recall that when Mark Kenoyer lectured at the Bead Museum about Indus Valley beads he spoke about a method he had for measuring the channels of ancient stone beads.
How do you suggest we measure? TIA, Paula