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SPI "Thread Mic" Outside Diameter Attachment & Insert Question


New member
I bought this set to use with 1-2" Mitutoyo Mic and need help with the setup/zero.

Instructions say :
-Set micrometer with standard (i.e. a 1-2" micrometer with 1" standard)
-Rotate spindle to .450 and zero display
-Place adapters on micrometer anvils

Do I need "standard" thread plug gauge to set it up or are they talking about the "standard" 1 inch. zero/setup gauge in the micrometer box?
The only way I can move to .450 is to go to INC mode and then my measurements are no where close. I'm sure it's something easy but the instructions aren't really that clear.


New member
I would read the instructions to mean that the anvils, if fully closed, are .450 thick.

It's harder if the mic isn't digital, but if you followed the instructions, zero set with the 1" standard first, open to .450 and zero set again, it should be ready to measure a thread. If the mic read .3425 (random number), it would say the pitch diameter of the thread is 1.3425, the max pitch diameter of a 1-3/8 - 20 UN thread.

Is it not working that way?