(Subject changed)
Alan,

On Thu, 22 Nov 2007 09:54:50 -0000, Alan B. Pearce wrote:

> >I'm not that familiar with posi-drive, a quick google shows it's a
> >trademark for snap-on?
> 
> I thought Posidrive was a company in itself, that owned the trademark. 
> Posidrive tools are certainly made under licence by many companies, of which 
> snap-on is probably one.

As far as I remember, Posidriv (sic) in the UK was produced initially by GKN some time in the late 60's or early 70's, and they sold the screws and screwdriver in a 
set.  The screws were unusual for the time, apart from the head design, in that they were hardened (mild steel was the norm), and had very sharp, high-angled 
threads which made them easier and faster to drive without a pilot hole.  There was only one size of head (now called PZ2) and a limited range of screw sizes (6, 
8, 10).  Later on, others started making them, increased the range of sizes of head (PZ0 to PZ3) and started using them for machine screws as well.  Someone else 
came up with "Prodriv" which is apparently compatible but avoids patent infringements somehow.
 
> >Pictures look like it's just another form of Phillips with
> >four additional "points", I suppose this reduces the chance
> >of stripping the head? I have seen them, but they've never
> >stuck out as being much better then Phillips.
> 
> The angle on the side of the flutes is different (steeper) and the point is 
> sharper. IIRC the flutes are also thinner. This is why Nate found getting 
> the correct tool for the screw made them much nicer to use. The extra 4 
> points are not actually functional AFAICT, but are there mainly to 
> distinguish the screw and tip from Phillips ones.

I believe they also enhance the stickability, so the screw stays on the driver unaided to allow one-handed operation - particularly useful in confined spaces and 
with electric drivers.  It was one of the selling points, and I remember the picture on the boxed-set was of a screw on the driver unsupported.  The shape also has 
more of a natural lead-in then Phillips, making it easier to engage by feel.
 
> I find the Posidrive is nicer to use than the 'ordinary' Phillips because of 
> these features, even when using the correct tip for the screw. 

It's rather hard to buy Phillips screws in the UK these days - Posi/Prodriv seem to have taken over in most places.  See the Screwfix web site 
(http://www.screwfix.co.uk).  Which makes it annoying that a lot of the gadget sets of quick-change bits you can get - particularly from America - have Phillips and 
slotted heads, but not Posi.

Personally I *never* use slotted screws these days - they are such a pain especially with electric drivers, and if I take out a slotted screw I replace it with a Posi.  
It's just annoying that some types of screws, notably round-head wood screws, are hard to find in anything other then slotted, for some odd reason.

I've only found the square-hole screws that were mentioned earlier (Robertson?) in pocket-joint kits (where you have a jig to drill a 2-diameter hole at about a 20 
degree angle in order to butt-joint wood - are they called Kreg?) where presumably it's easier to engage "blind" deep in the hole.

Cheers,


Howard Winter
St.Albans, England


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