For drilling an accurate hole in overlapping sheets. The inverted type duplicator allows you to locate a hole from the back of an overlaping sheet. #10 #21 #30 #40 1/4" drill sizes, 6-1/4" or 13-1/4"
PN 12-01507 is pictured.
WARNING: The product may contain and/or expose you to a chemical(s) or substance(s) which are known to the State of California to cause cancer and/or birth defects or other reproductive harm. www.P65Warnings.ca.gov
My fault for not looking at the picture more carefully before buying. The description even says INVERTED TYPE. The tool is quite well made but not what I expected or wanted. I have not come across a use for this type of strap duplicator yet but for the price of the tool relative to the shipping I will just keep them and see if a need ever comes up.
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Instrument screws are usually a 6-32 so you would want a #35 bit. I would go with the number 30 duplicator to make the initial hole and then follow up with a #35 drill.