Interesting. When looking at this I tripped over another DEC related item: http://www.ebay.com/itm/DEC-DIGITAL-EQUIPMENT-CORPORATION-REEL-GO-NOGO-GAUG… I'm not sure what you'd use it for unless you were manufacturing DECtape reels, but it certainly is interesting. You could make one yourself, if you have a lathe and the ability to hold tight tolerances. One of the photos actually shows the dimensions as written on the gauge. paul