Posted by Clive Hartland on 14/01/2016 16:44:14:
Tried an M5 plug tap in the hole and no joy …
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Clive,
Just a note of caution [Teaching Granny to suck eggs ?]
As you will see from the excellent diagram and notes here; It is possible to have a 'within spec' Tap which does not freely fit an existing 'within spec' female thread. … The Devil is in the detail [that little white 'optional' area at the top of the diagram].
Assuming that it's an M5 x 0.8 Tap … Have you tried using it as a thread gauge, laid against the grubscrew?
MichaelG.
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Edit: [a useful Quote from the Wikipedia text; with my added emboldening] … "Conversely, in an internal (female) thread (e.g., in a nut), the major and minor diameters are minimum dimensions, therefore the thread profile must end flat at Dmin but may be rounded out beyond Dmaj."
Edited By Michael Gilligan on 15/01/2016 09:48:58