enter image description here Here in this book of Theory of machines by S.S. Rattan it is written that diametral pitch is not used in S I units. Why is that so?

  • $\begingroup$ Because the term 'Diametral pitch ' is defined as the number if teeth per inches and not meter or millimetre. As you know all gears are normalised so it doesn't' make any sense to define this term in S.I units. I think that's the reason. $\endgroup$
    – user14407
    Commented Aug 25, 2018 at 12:34
  • $\begingroup$ That's a very frustrating cropping of the text photo. $\endgroup$
    – Transistor
    Commented Apr 22, 2019 at 21:51

1 Answer 1


European standards differ from US standards. US standards re not generally SI based. European standards have defined module, then therefore there is no need to define a second set of definitions.


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