# Hex Head Bolt tool sizes **URL:** \ **Category:** Factual Questions\ **Created:** [February 3, 2017, 1:08pm UTC](https://boards.straightdope.com/t/hex-head-bolt-tool-sizes/778898 "2017-02-03T13:08:37Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [February 4, 2017, 11:33pm UTC](https://boards.straightdope.com/t/hex-head-bolt-tool-sizes/778898/21 "2017-02-04T23:33:51Z")
> [@Toledo\_Jim](#): > > If it’s any consolation, OP, there was once a system of fasteners just like that: Whitworth. A wrench marked “1/2” was the proper size for a fastener (bolt or nut) with a “1/2” thread. The actual size of the wrench (across flats) opening was something just north of 11/16". Sir John Whitworth invented what he thought was an ideal relationship between the thread and the head of a nut or bolt. He apparently convinced some of the English carmakers to use his system. He somehow managed to make sure that few, if any, of my existing SAE or metric wrenches would work. And when the Whitworth system was replaced with the British thread sizes, tool manufacturers went to the modern wrench sizes. All these early wrenches are marked 1/2 AF or 3/4 AF or whatever. This means “across the flats” and indicates the marked wrench size is the actual opening, not the previous bolt size. All the wrenches for my TR3 are AF wrenches. Dennis ---
**Author:** ![Bones\_Daley](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@Bones\_Daley](https://boards.straightdope.com/u/Bones_Daley)\ **Post date:** [February 5, 2017, 12:29am UTC](https://boards.straightdope.com/t/hex-head-bolt-tool-sizes/778898/22 "2017-02-05T00:29:53Z")
> [@Toledo\_Jim](#): > > Sir John Whitworth invented what he thought was an ideal relationship between the thread and the head of a nut or bolt. Who him ? Any relation to Sir **Joseph** Whitworth, the renowned English engineer ? ---
**Author:** ![seal\_cleaner](https://avatars.discourse-cdn.com/v4/letter/s/e274bd/32.png) [@seal\_cleaner](https://boards.straightdope.com/u/seal_cleaner)\ **Post date:** [February 5, 2017, 3:20am UTC](https://boards.straightdope.com/t/hex-head-bolt-tool-sizes/778898/23 "2017-02-05T03:20:49Z")
> [@Joey\_P](#): > > Am I the only person that just eyeballs the bolt (head), grabs the appropriate tool (wrench/socket in this case), then when it doesn’t fit, grabs a different one, then when that doesn’t fit, grabs TWO more and wonders if I should brings the whole set over so I don’t have to walk up and down the stairs so many times, no, between these two, one of them will fit, right, wrong, bring the whole set up, we’ll get there eventually, hopefully. > When I’m finally done, I have to really convince myself that it’s better to sit there and snap all these sockets back into place than to just toss them on top of the open box and be done with this stupid project. Am I the only guy who just puts the socket any damn place into the case, and then has to repeat the whole process next time? They’re all marked, why can’t I take the time to put them into the right slot? ---
**Author:** ![wolfman](https://avatars.discourse-cdn.com/v4/letter/w/a8b319/32.png) [@wolfman](https://boards.straightdope.com/u/wolfman)\ **Post date:** [February 5, 2017, 4:23am UTC](https://boards.straightdope.com/t/hex-head-bolt-tool-sizes/778898/24 "2017-02-05T04:23:56Z")
> [@seal\_cleaner](#): > > They’re all marked, why can’t I take the time to put them into the right slot? Probably because you, like me, once bought a set with good hardware and a shitty case, and after you spent the time to put them all into the correct slot, an accidental drop of a billionth of an inch(metric:bizilometer) cause them all to pop out and end up a pile the next time anyway. ---
**Author:** ![Toledo\_Jim](https://avatars.discourse-cdn.com/v4/letter/t/34f0e0/32.png) [@Toledo\_Jim](https://boards.straightdope.com/u/Toledo_Jim)\ **Post date:** [February 6, 2017, 12:01am UTC](https://boards.straightdope.com/t/hex-head-bolt-tool-sizes/778898/25 "2017-02-06T00:01:31Z")
Oops. Yes, that would be Joseph Whitworth. Sorry [Previous page](https://boards.straightdope.com/t/hex-head-bolt-tool-sizes/778898.md?page=1)