Internal thread calculations

[Howard LewisParticipant @howardlewis46836]

The theoretical bore size probably does not take any account of the rounding or truncation of the nbthread (To prevent root/crest conflict)

Hence the (Nominal diameter – Pitch) provides the clearance, and a % thread engagement that suffices for most purposes.

Being an internal thread, it is not possible to measureb over wires, so an external GO/NO GO gauge would mneed mto be made, sized by measuring over wires.

IF such precision is really required.

For a 33mm Coarse thread, (3 mm pitch) Zeus charts quote 28.706 mm as the core diameter, but a 29.5 mm tapping drill. Using the “Nominal – Pitch”, the tapping drill would be 30 mm)

On this basis, a 32 x 2 mm thread (Not listed as a standard Metric Fine thread in Zeus) would be also be bored / drilled 30 mm.

There should be no root/crest interference and the % engagement should provide sufficient strength for most purposes.

Howard

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