# What kind of bolt is this?
**URL:** https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081
**Category:** Factual Questions
**Created:** [June 6, 2005, 2:33am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081 "2005-06-06T02:33:53Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)
#### Post date: [June 6, 2005, 2:33am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/1 "2005-06-06T02:33:53Z")
So today I’m working on the engine in my 1991 Pontiac Sunbird. In order to replace a short section of hose, I need to remove the oil dip stick tube / oil vent assembly.
The assembly mounts to the engine using small two bolts. At first I thought they were Torx bolts, so I grabbed a Torx T40 bit driver and tried to remove them. It didn’t work.
So I started to take a closer look at the bolt heads on these two bolts. It sort of looks like a Torx bolt head (the center of the bolt head is recessed with “teeth” along the inside circumference), but instead of 6 points there are 12! That’s right… a bolt head with a star-like _recessed/female_ pattern with 12 points.
I knew a Torx bit driver wouldn’t work, so I tried a regular 6-point hex head driver(a.k.a. Allen wrench) on one of the bolts. A 6 mm 6-point hex head driver seemed to fit O.K., but I didn’t try loosening it for fear that I would strip the inside of the bolt head.
So what kind of bolts are these?? I did some google searches but came up empty-handed. More importantly, how do I remove them? Is there a special 12-bit male driver I should use? Or should I use a 6-point hex bit?
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### Author:  [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)
#### Post date: [June 6, 2005, 2:44am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/2 "2005-06-06T02:44:40Z")
Anytime there’s a Tprx or Torx-like head with an even number of points and no center pin, I’ve found you can use a flathead screwdriver. Select the largest one that fits inside the head depression.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [June 6, 2005, 2:45am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/3 "2005-06-06T02:45:04Z")
It’s a [bihexagon head](http://www.google.com/search?hl=en&lr=&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&q=%22BIHEXAGON+HEAD%22&btnG=Search).
There are special wrenches for them.
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### Author:  [@AtomicDog](https://boards.straightdope.com/u/AtomicDog)
#### Post date: [June 6, 2005, 2:46am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/4 "2005-06-06T02:46:13Z")
It’s a self-sealing stem bolt.
What?
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### Author:  [@gerb](https://boards.straightdope.com/u/gerb)
#### Post date: [June 6, 2005, 2:48am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/5 "2005-06-06T02:48:35Z")
It may be a “spline Drive”. I have seen them on German cars but they are usually a
larger bolt.
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### Author:  [@dqa](https://boards.straightdope.com/u/dqa)
#### Post date: [June 6, 2005, 2:56am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/6 "2005-06-06T02:56:58Z")
From the images at the Google search of Bihexagon, that term appears to apply to a “male” bolt head.
What Crafter\_Man describes I have heard referred to as a [triple square](http://shop.metalnerd.com/index.cgi?code=3&cat=5) or twelve point bolt. The latter term is tougher to search, because of the twelve point wrenches for normal nuts and bolts.
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### Author:  [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)
#### Post date: [June 6, 2005, 2:59am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/7 "2005-06-06T02:59:29Z")
Why use such an odd piece?
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### Author:  [@Rick](https://boards.straightdope.com/u/Rick)
#### Post date: [June 6, 2005, 3:09am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/8 "2005-06-06T03:09:58Z")
Old German cars used to be triple-square happy. Manifolds, head bolts were commonly tripple square on non-VW cars of the 60-70.
I have (IIRC) them in 6mm, 8mm, 10mm, and 12mm.
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### Author:  [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)
#### Post date: [June 6, 2005, 3:55am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/9 "2005-06-06T03:55:53Z")
> [@Rick](#):
>
> Old German cars used to be triple-square happy. Manifolds, head bolts were commonly tripple square on non-VW cars of the 60-70.
> I have (IIRC) them in 6mm, 8mm, 10mm, and 12mm.
Every Benz, Beemer, or Beetle that I owned was from the sixties, and all repairs were accomplished with ordinary metric sockets. I fear **Crafter\_Man** has a different beast on his hands.
How about checking out MSC Industrial Supply online, or Snap-On to source the proper driver bit?
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [June 6, 2005, 11:57am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/10 "2005-06-06T11:57:04Z")
Here’s a catalog photo of a 10mm version of a spline drive, common on German cars, particularly Porshe. [http://www.zdmak.com/wbstore/main.asp?action=PROD&PROD=ZV-5800VX10&CTMP=1&LowCt=0](http://www.zdmak.com/wbstore/main.asp?action=PROD&PROD=ZV-5800VX10&CTMP=1&LowCt=0)
I don’t know what other sizes they may sell.
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### Author:  [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)
#### Post date: [June 6, 2005, 12:37pm UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/11 "2005-06-06T12:37:49Z")
> [@dqa](#):
>
> From the images at the Google search of Bihexagon, that term appears to apply to a “male” bolt head.
>
> What Crafter\_Man describes I have heard referred to as a [triple square](http://shop.metalnerd.com/index.cgi?code=3&cat=5) or twelve point bolt. The latter term is tougher to search, because of the twelve point wrenches for normal nuts and bolts.
Yea, it looks like that might work.
As mentioned, I also shoved a 6 mm hex bit (“Allen wrench”) into the bolt head, and it seemed to fit. Do you think these heads were also designed to accommodate hex bits? If you think it would work, I could purchase a 6 mm hex driver and try it.
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### Author:  [@Padeye](https://boards.straightdope.com/u/Padeye)
#### Post date: [June 6, 2005, 3:02pm UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/12 "2005-06-06T15:02:53Z")
Do not use a hex bit, you’ll likely damage the bit and possibly even worse the bolt. Since the patter is three squares the corners are by definition 90º. A hex bit has 120º corners that will not get a proper grip in the bolt. I haven’t had to use one of these in a long time but remember easily finding them when I pulled the cylinder head from my old VW Rabbit.
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### Author:  [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)
#### Post date: [June 6, 2005, 4:31pm UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/13 "2005-06-06T16:31:26Z")
Thanks for all the responses.
I’m going to purchase this set and use the 6 mm bit:
[http://www.lislecorp.com/tool\_detail.cfm?detail=1080](http://www.lislecorp.com/tool_detail.cfm?detail=1080)
If it doesn’t work I’ll try a 6 mm hex bit.
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### Author:  [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)
#### Post date: [June 6, 2005, 5:07pm UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/14 "2005-06-06T17:07:22Z")
BTW: I did another google search and found something called a **double hex** or **double hexagon** bit:
[http://www.autopart.com/TOOLS/TOOLSMAIN/tool/T\_9288.htm](http://www.autopart.com/TOOLS/TOOLSMAIN/tool/T_9288.htm)
[http://www.cooperpowertools.com/brands/apex/form/index.cfm?fuseaction=socket\_form](http://www.cooperpowertools.com/brands/apex/form/index.cfm?fuseaction=socket_form)
[http://www.mactools.com/content/ecatalog/SP\_Section\_2004\_MT\_Catalog.pdf](http://www.mactools.com/content/ecatalog/SP_Section_2004_MT_Catalog.pdf) (bottom of page SP-45)
[http://www.ozat.co.il/asg/Item\_213.html](http://www.ozat.co.il/asg/Item_213.html) (bottom of page)
Is a double hex the same thing as a triple square?
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### Author:  [@awldune](https://boards.straightdope.com/u/awldune)
#### Post date: [June 6, 2005, 6:25pm UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/15 "2005-06-06T18:25:49Z")
> [@Crafter\_Man](#):
>
> Is a double hex the same thing as a triple square?
No, because the angles are different. This is the same as using a regular hex bit, except that you would be touching all 12 points instead of just 6. If the hex bit fit in your bolts, maybe your bolts are double hex and not triple square?
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### Author:  [@Padeye](https://boards.straightdope.com/u/Padeye)
#### Post date: [June 6, 2005, 11:31pm UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/16 "2005-06-06T23:31:06Z")
> [@Crafter\_Man](#):
>
> Is a double hex the same thing as a triple square?
Perhaps [this](http://www.pimacountychoppers.com/images/12point.jpg) will help explain how they are different and why not to use hex and double hex keys in triple square bolts.
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### Author:  [@jayjay](https://boards.straightdope.com/u/jayjay)
#### Post date: [June 6, 2005, 11:47pm UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/17 "2005-06-06T23:47:04Z")
> [@AtomicDog](#):
>
> It’s a self-sealing stem bolt.
>
> What?
Geeeeeeeeeeeek!
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### Author:  [@tracer](https://boards.straightdope.com/u/tracer)
#### Post date: [June 7, 2005, 12:06am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/18 "2005-06-07T00:06:08Z")
I’ll give you 3 strips of gold-press Latinum for the stem bolt set.
But only if they really are self-sealing.
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### Author:  [@jasonh300](https://boards.straightdope.com/u/jasonh300)
#### Post date: [June 7, 2005, 12:06am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/19 "2005-06-07T00:06:25Z")
> [@Crafter\_Man](#):
>
> The assembly mounts to the engine using small two bolts. At first I thought they were Torx bolts, so I grabbed a Torx T40 bit driver and tried to remove them. It didn’t work.
Why don’t you call the service dept. at your local Pontiac/GM dealership and ask?
They’ll probably be able to tell you exactly which bit you need and what size. They’ll probably even try to sell it to you although the price is going to be inflated.
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### Author:  [@jasonh300](https://boards.straightdope.com/u/jasonh300)
#### Post date: [June 7, 2005, 1:08am UTC](https://boards.straightdope.com/t/what-kind-of-bolt-is-this/307081/20 "2005-06-07T01:08:47Z")
Another suggestion would be to catch the local Snap-On or Mac Tools guy and he’ll probably have the tool on his truck if you can show him the bolt.