On 2012-08-09, Percival P. Cassidy wrote:
> On 08/09/12 02:12 am, Mark Brader wrote:
>
>>>> Not being a sailor, the most familiar use of "purchase" (meaning
>>>> "gripe") to me is a description of a screwdriver mating with a screw.
>>>> We speak of "lack of purchase" when the screwdriver slips in the
>>>> opening of the screwhead.
>
>> Peter Brooks:
>>> That's very polite of you, most people say 'fuck' as it loses purchase
>>> and enters the fleshy part of the hand.
>>
>> Some of us say "When will those Americans learn to supply Robertson-head
>> screws instead of Philips?"
>
> Robertson are OK, but I prefer Torx.
The problem with Torx is that you have to have *exactly* the right
size driver handy for the screw head, whereas you can often get by
with a #2 Philips driver in a #1 head (for example).
> PoziDrv are better than Phillips,
> but most Americans have never heard of them even though PZ bits often
> come as part of a set of assorted bits sold in US stores. Just try
> buying a PoziDrv screwdriver in the US; the only one I have is a UK-made
> one I bought while on vacation in NZ.
It was only recently that I discovered the extra marks let you
distinguish Philips & PZ without trying a screwdriver & hoping for the
best!
http://donsnotes.com/home_garden/images/pozi.gif
> It was only recently that I discovered that Phillips heads and bits were
> *designed* so that the bit "cams out" -- to avoid overdriving the screw.
> But the designers seem to have overlooked the possibility that a screw
> may become tighter after a while, whether due to corrosion or some other
> cause; thus the bit may cam out before the screw loosens.
IIRC, they were designing the heads & drivers for assembly line use in
the days before torque limiters on electric screwdrivers --- so
getting the blasted things back out was a low priority.
--
Civilization is a race between catastrophe and education.
[H G Wells]