Nominal sizes?

[Bo’sunParticipant @bosun58570]

Good morning,

Nominal sizes, in this case with respect to tooling, can often be confusing.  Because, without any source of reference, are in many cases meaningless.

For example:  I want to buy a pair of dividers (larger than the ones I already have), but when the stated size is say 4″, is that from the pivot, is it the overall length, or some other dimension?

Your views, knowledge or comments appreciated.

[noel shelleyParticipant @noelshelley55608]

I think you have answered your own question – meaningless ! At least in this context ! Only by asking the supplier will you have any idea, the only thing you know is that, in theory, a 4″ will be bigger than a 3″. The only time I have used Nominal sizes is with steel tube, where the  size range is within limits laid down in tables. Noel.

[Speedy Builder5Participant @speedybuilder5]

You could look at this ?

https://technologystudent.com/equip_flsh/springdiv1.html

https://technologystudent.com/equip_flsh/springdiv1.html

[CirclipParticipant @circlip]

Wonder what nominal size would be applied to a 12″, SORRY 300mm Rule? (NOT RULER). I own a 12″ Eclipse hacksaw and also a 6″ Phillips Junior version, Both longer than the description.

Regards  Ian.

[Circlip]

On Circlip Said:

Both longer than the description.

Perhaps if you could read ‘nominal’ as ‘characteristic’, your confusion would disappear.

A hacksaw is described by the blade it can accommodate. A BSP thread is described by the (nominal) pipe ID.

How are Coventry die heads described? How are Stilson spanners described? I tried my 18″ stilsons on a piece of 4″ diameter pipe and the jaw fell out.

[noel shelley]

On noel shelley Said:

the only thing you know is that, in theory, a 4″ will be bigger than a 3″.

“In theory” being the operative word.

 

[JasonBModerator @jasonb]

Moore and Wright ones are measured from pivot to point.

[Bo’sunParticipant @bosun58570]

Thanks Jason.  That gives me a better idea of what I should be looking for.  That said, maybe the capacity (maximum arc) might be more useful?

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