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There is a belief that wrench size is the across the flat distance of a bolt head/nut. any reason other than this for designing wrenches in these standard sizes?

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closed as off-topic by Ralph J, J Walters, mins, curious_cat, aeroalias Jan 31 '16 at 5:20

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about aviation, within the scope defined in the help center." – Ralph J, J Walters, mins, curious_cat, aeroalias
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Welcome to Aviation.SE! For aircraft designed and built in the USA, yes, this is the standard for hardware and tooling. The reasons are not particular to aviation, but have to do with the standards of measurement and the history of industrial development in the US. $\endgroup$ – J Walters Jan 31 '16 at 2:24
  • $\begingroup$ Seems to be related to Renard's series, further detailled on Wikipedia. $\endgroup$ – mins Jan 31 '16 at 13:07
  • $\begingroup$ Because a wrench wouldn't work if it didn't match the bolt head. Bolts and (wrenches to fit them) come in standard sizes because... Well, can you imagine the confusion if they were all different? It's bad enough keeping Imperial and metric straight. $\endgroup$ – jamesqf Jan 31 '16 at 19:12
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Spanners and all hand tools are based on the bolt head size, eg, 3/8" across the top of the flats of the bolt head, note, this is not the bolt shank size, the threaded part. Because most widespread use of tools began in the US, the Imperial system of tool sizing came from there. In the last 30 or so years, the metric system has become widespread, but as aviation is largely based on the US system, the imperial system of measurement largely remains. There were some other forms of tool measurements uses, the UK BAE and Whitworth sizes but fortunately, these never became widespread, otherwise, your toolbox became a nightmare of tool sizes. Yes, been there, had that.

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    $\begingroup$ "most widespread use of tools began in the US" [citation needed] $\endgroup$ – David Richerby Jan 31 '16 at 5:24
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    $\begingroup$ @DavidRicherby <looks up from bashing large rock with small rock> Unga-Bunga? $\endgroup$ – voretaq7 Jan 31 '16 at 5:41
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    $\begingroup$ Because most widespread use of tools began in the UK during the industrial revolution when the imperial measures of tools were invented - there, fixed it for you. $\endgroup$ – Simon Jan 31 '16 at 14:12

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