Twisted Hex Screwdriver Tip

[Jabberwocky]

Is anybody familiar with a twisted hex tip for screwdrivers? The idea is that the hex (think allen wrench) has a slight twist to it to retain the screw. We have been using tapers in the past but have heard that twists may be less susceptible to wear.

Are there any standards for this kind of thing? Does the geometry have a specific name that I should search for?

Thanks.

 

[Fabrico]

That does not sound very convincing, but, nor have I seen them. There is also the Bondhus Prohold hex wrenches that use a little nylonish knob at the end for bolt retention.

 

[MintJulep]

Never seen a twisted hex drive that was twisted on purpose.

Lots of info on these:

http://www.wihatools.com/pro_magicRing.htm

 

[swall]

Just a guess. Many splined CV joint stems have a slight helix, rather than being straight. The helix is not noticeable upon casual examination of the spline and allows for a snug fit in the female spline. Could be doing the same thing to a hex.

 

[Jabberwocky]

FYI, we've since discovered this fitting is referred to as a 'captive twist'.

 

[Screwman]

The problem with the twisted tip is that it is dependent on having quite a deep and tight recess to function properly. If the fastener has a lower head (pan or truss) then the depth of the recess isn't enough to engage the twist at it extremes. We played with this system when we were working on a way to make parts stick onto bits and it was not one of the winners. The other problem is that because you have point contact at just the tip and top of the recess you tend to get a lot of wear in those locations, so the bit life isn't real good.
The other thing that happens when there is enough twist to get the parts to stick in shallow recess parts is that the bit now wants to cam out when driven in the opposite direction.

Dick

 

[Jabberwocky]

Good points, could you tell me more about what system won? If you're at liberty to divulge of course.