# why standard wrenches are sized like 1“,15/16”,7/8“,1/4” etc? [closed]

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?

• 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. – J Walters Jan 31 '16 at 2:24
• Seems to be related to Renard's series, further detailled on Wikipedia. – mins Jan 31 '16 at 13:07
• 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. – jamesqf Jan 31 '16 at 19:12

• 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. – Simon Jan 31 '16 at 14:12