# Why are 7 mm Allen wrenches so rare? **URL:** \ **Category:** Factual Questions\ **Created:** [August 23, 2011, 4:09am UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747 "2011-08-23T04:09:23Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![633squadron](https://avatars.discourse-cdn.com/v4/letter/6/ee59a6/32.png) [@633squadron](https://boards.straightdope.com/u/633squadron)\ **Post date:** [August 23, 2011, 4:09am UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/1 "2011-08-23T04:09:23Z")
If you’re a Maker type like me, you know that Allen wrenches are an indispensable item in the modern toolbox. I ride both bicycles and BMW motorcycles, so I know that having the right metric Allen wrench is critical. I recently bought an add-on part for my motorcycle that attaches with a 7 mm Allen wrench. I happened to have one in my toolbox, but I started shopping for an extra one to carry in my on-the-bike toolkit. I discovered that 7 mm Allen wrenches are more rare than chicken’s teeth. This is widely known; in fact, some companies think of this as a _feature_, since using a 7 mm hex head screw almost guarantees that nobody besides you will be able to remove it. Why is 7mm so rare, though? As far as I can tell, sizes from 2mm through 10mm, including 2.5 and 5.5, are common, but nearly every set I’ve seen skips 7. Is this one of the secrets of the Trilateral Commission?:eek: Does it have some mystical Hermetic explanation? ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [August 23, 2011, 5:27am UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/2 "2011-08-23T05:27:17Z")
I see a lucrative niche market… Who does the "Sham-Wow " commercials, I got an idea… ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [August 23, 2011, 10:44am UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/3 "2011-08-23T10:44:44Z")
I tend to blame the French and the ISO for any such troubles. I once read that there are 2 different sets of metric standards. So sets of wrenches made for one, lack sizes commonly used by the other. This was pointed out to me when I was complaining about a lack of 15 mm wrenches and sockets and wrench sets having a 16 mm wrench thant doesn’t fit much but 5/8’’. My truck and the cars I have had since metric became common all have a bunch of 15 mm nuts. By the way, the set Craftsman Allen wrenches I bought 30 years ago does have a 7 mm. ---
**Author:** ![Mops](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mops/32/16494_2.png) [@Mops](https://boards.straightdope.com/u/Mops)\ **Post date:** [August 23, 2011, 11:24am UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/4 "2011-08-23T11:24:49Z")
M8 screws with socket heads take a 6 mm key, and M10 screws take a 8 mm key. M9 threads are unusual. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [August 23, 2011, 2:16pm UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/5 "2011-08-23T14:16:47Z")
So rare, it can be found in 11 seconds: [http://www.sears.com/shc/s/p\_10153\_12605\_SPM1921893701P?blockNo=10&blockType=G10&prdNo=10&i\_cntr=1314108965961](http://www.sears.com/shc/s/p_10153_12605_SPM1921893701P?blockNo=10&blockType=G10&prdNo=10&i_cntr=1314108965961) ---
**Author:** ![Jmachjr](https://avatars.discourse-cdn.com/v4/letter/j/77aa72/32.png) [@Jmachjr](https://boards.straightdope.com/u/Jmachjr)\ **Post date:** [October 21, 2020, 2:47pm UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/6 "2020-10-21T14:47:12Z")
Was thinking it was a japanese thing as they avoid odd numbers and the number 7 is especially bad but that would be a huge conspiracy lol ---
**Author:** ![its\_the\_daddy](https://avatars.discourse-cdn.com/v4/letter/i/bb73d2/32.png) [@its\_the\_daddy](https://boards.straightdope.com/u/its_the_daddy)\ **Post date:** [October 21, 2020, 7:13pm UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/7 "2020-10-21T19:13:36Z")
7mm hex socket head screws are common on European cars, specifically being used for the pins on which sliding brake calipers slide: on Ford and VAG cars to my certain knowledge. This has been so for many, many years. To the extent that the 7mm Allen key is commonly sold as a ‘special tool’ for brake calipers by Halfords accessory shops and others. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [October 21, 2020, 7:50pm UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/8 "2020-10-21T19:50:31Z")
A 7mm hey key is so close to the 71/256" that everyone has their toolbox that you don’t need the metric version. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [October 21, 2020, 8:12pm UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/9 "2020-10-21T20:12:02Z")
[Allen Manufacturing Company](https://en.wikipedia.org/wiki/Allen_(brand)) (now owned by Apex Tool group) must be very happy that everyone calls [hex keys](https://en.wikipedia.org/wiki/Hex_key) “Allen keys.” 🙂 ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [October 21, 2020, 8:47pm UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/10 "2020-10-21T20:47:21Z")
As happy as that guy Phillip and his screwdriver. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [October 21, 2020, 10:51pm UTC](https://boards.straightdope.com/t/why-are-7-mm-allen-wrenches-so-rare/593747/11 "2020-10-21T22:51:11Z")
So maybe they were rare 11 years ago, but even the basic set of keys the I got at Lowes has a 7mm. However, the “army knife” style with multiple fold-out keys in a handle does not.