Osy;
Welcome to the forum. I did not see your post until now; I guess I do not hang here enough.
I have threaded plug gage M8x1.25-6H. What tolerance do I use for this gage?
The tolerance for the gage is given in the thread designation. You need to have the details for the 6H class-of-fit.
Where do I find the tolerances?
Like smkeilman said?
The dimensions for metric M-profile thread plug and ring gages are found in ANSI/ASME B1.16M.
This is the originating source for this data, so it is the best place to obtain your information; however; it is tedious reading. He also indicated:
Machinery's Handbook contains information regarding how the dimensions and tolerances are calculated.
I agree that the Machinery?s Handbook is a good book for general information about product screw threads, but I would not use it as a source for calibration data for your thread gages.
The easiest place to get the information you need is off the original gage certification; provided you purchased the Long Form Certification (the detailed inspection report).
If you did not purchase the LFC or it was not maintained in the gage records, then the next best thing is to use ThreadTech software. ThreadTech Software has the capability of producing the gage requirements for many thread standards and likely all that you will need in your shop.
Here is a link for a Free 30-day trial Version of ThreadTech software.
Smkeilman is again correct?
? typically one would use calibrated best size thread wires and the three wire method. Your Supermic should be adequate to take the measurements.
If you sent your thread plug gages to a professional calibration laboratory they would be using a Supermic of some sort with thread wires to do the measurement.
? is it possible to use a threaded ring gage to calibrate the M8 gage above?
My supervisor said I could use a threaded ring gage to calibrate the M8 plug gage. Is this true?
That is totally false. According to B1.16m the only valid method of testing thread plug gages is wires with some measurement tool. Some people come to us to buy master ring gages made to special pitch diameters specifically to calibrate their plug gages. Think on that for a minute; you use a special ring gage to calibrate your thread plug gage, but what do you use to calibrate the ring gage? That is right; a plug gage. See the circular logic in that? (If it were a tapered pipe thread plug gage, then you do use a tapered ring gage to calibrate it; but we are not talking pipe threads here.)
Here is a link to a page where you will find wire sizes and associated constants for many common thread sizes (UN-series; M-series; ACME-series)
