Prowler V6

[Gary Derian]

The original US metric thread standard actually had a 6.3 mm thread.  This
was coincidentally exactly 1/4 inch.  They did it so the jump in strength
going up one size would be consistent.  Needless to say this was a bad idea.
A 6.3mm nut fit perfectly on a 6mm bolt with only 1/3 the strength.

BTW, I always wondered what the 19/32 and 23/32 Craftsman wrenches were for.
Are they collectables now?  I can't wait for The Antiques Road Show to come
to town.

Cheap Asian copys of equipment copy everything, right down to the English
threads except they can't get inch hex stock locally so they use metric.

Gary Derian <gderian at oh.verio.com>


> There are four "standards" for fasteners. They relate to the thread pitch
> more than anything although there are several different "head" sizes.
Mostly
> the Japanese/asian use 10, 12, 14, 17, 21, & 32. The europeon use 10, 13,
> 14, 17, 19, 21 and various larger sizes. Other than the English. They used
> to use what was called a Whitworth standard. These are the 3/8 bolts with
> the "15mm" heads. Actually they are 19/32. They also used 23/32 (i think
it
> was.) I haven't seen those wrenches since my tools were stolen. You used
to
> get them in every Craftman set up until about 1975.  You will also notice
> that most, nearly all, of the English bolts are a "fine" thread pitch. It
> isn't quite the same as SAE fine as the radius of the thread root is
> different and although you can use one on the other they ussually are a
very
> tight fit and sometimes destroy the fasteners. Then of course you have SAE
> standard inch sizes and the famous SAE standard metric sizes. Other than
the
> 15mm the 16 and 18 are so close to SAE 5/8 and 11/16 that many times you
can
> use these sizes to remove them. Maybe had something to do with it at the
> start.
>
> Just my .02$
>
> Scott