In article , "JerryMouse" wrote:

That's not it. Robertson bits/screws are denominated in metric. We use
Imperial measures. Except for spark plugs, of course.

Huh?

1) Robertson screwdrivers are denominated as #0, #1, #2, #3, etc just like
Phillips screwdrivers. Metric has nothing to do with it.

2) Robertson screws come in the same variety of sizes and lengths as any other
screw, and are denominated in exactly the same fashion, e.g. a 6-32 x 3/4"
machine screw.

3) Metric dimensions and labelling have not proven to be an impediment to the
importation, manufacture, and use in the U.S. of plenty of metric bolts and
wrenches.

4) The spark plugs most widely used in the U.S. have 5/8" or 13/16" hex heads.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?