<VV> 'Hour-glass' head screws?

[William Hubbell]

Hugo,

I think you are confusing the more modern “one-way” screw with the older, now largely obsolete “bow tie” screw.  The “bow tie” was indeed called a clutch head screw and that designation can still be found on many sites.

This Wikipedia article clearly distinguishes between the two. 

https://en.m.wikipedia.org/wiki/List_of_screw_drives



Bill

> On Jan 2, 2020, at 8:49 AM, Hugo Miller via VirtualVairs <virtualvairs at corvair.org> wrote:
> 

That's a rather confused article - not least because it keeps referring to screws as 'rivets'. But a 'clutch-head', as the name implies, has a drive that works one way but not the other, for security purposes. The 'hour-glass' slotted screws that hold on the shield over the throttle cable, for example, do not have any sort of clutch, nor are they security fasteners. After all, who is going to steal a throttle cable? You can, if you're lucky, undo them with a screwdriver, but I had to grind down an allen key to undo some of mine.
So two questions - why on Earth would GM use such a fastener in routine positions on Corvair vans, and what is their proper name?



> On 2020-01-02 12:54, R wrote:
> http://blog.mutualscrew.com/2015/07/07/salient-features-of-clutch-head-screws/
> [2]
> 
> Ray
> 
> On Jan 2, 2020, at 2:15 AM, Hugo Miller via VirtualVairs
> <virtualvairs at corvair.org [3]> wrote:
> 
>> A clutch head is a 'one-way' security screw that you can tighten
> but
>> not undo. What are those weird 'hour-glass' head screws on the 95?
>> I've just been wrestling with some of them while changing the
>> throttle cable on my Corvan. I had to grind down an Allen key to
>> undo them. Luckily they weren't too tight nor corroded in place.
> Why
>> would they use such an unusual head - I don't think I've ever seen
>> them before?
>> 
>>> On 2020-01-02 02:43, FrankDuVal via VirtualVairs wrote:
>> 
>>> I have not been into a heater switch. Should be similar to other
>> 
>>> switches, like the windshield wiper or turn signal of an early.
>> 
>>> 
>> a href="https://www.google.com/search?q=fillister+h
>> 
>>> er&aqs=chrome
>> 9j0l6.3257j1j4&sourceid=chrome&ie=UTF-8">https://www.google.c
>> 
>>> 
>> 
> ad+screw&oq=Fillister&aqs=chrome.2.69i57j35i39j0l6.3257j1j4&sourceid=chrome&ie=UTF-8
>>> 
>>>> 
>>> 
>>>> The hourglass drive is a "clutch head" design.
>> te>https://www.google.com/search?q=cl
>> 
>>> q=clutch+head+fastener&aqs=chrome..69i57j0l7.4482j1j7&s
>> e&ie=UTF-8
>> 
>>> Commonly found on the interior sheet metal of a Corvair 95. And
>>> 
>>>> inside the Powerglide.
>>> 
>>>> 
>>> Frank Du
>>> 
>>>> te>
>>> br
>>> 
> 
> 
> Links:
> ------
> [1] mailto:VirtualVairs at corvair.org
> [2]
> http://blog.mutualscrew.com/2015/07/07/salient-features-of-clutch-head-screws/
> [3] mailto:virtualvairs at corvair.org

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