Q: (Initially posted on 9/4) FROM MENTEE AMANDA T. IN MO
Why on a new loaf of bread the twist tie turned to the
left instead of to the right, when normally when you
twist something you turn to the right and untwist to
the left? Dad says this makes a difference to those
who can't see as well to tell which way the twist tie
is twisted.

September 5, 2002
A: FROM MENTOR MOLLY WILLIAMS. FOR BIO. CLICK HERE.
It's a right-handed world! Most of the things we twist are made to
come off with a counterclockwise rotation. We're all accustomed to
expect right handed screw threads. That means that if you point
your right thumb in the direction you want something like a screw,
nut, or jar lid to move, then your fingers will curve in the
direction you need to twist. For example if you want to remove the
lid from a jar that's sitting upright, you point your right thumb
upwards (the direction you want the lid to come off); you'll see
that your fingers are pointing in a curve that goes
counterclockwise. That rule works equally well if you choose to
hold the lid steady, and rotate the jar instead. Your right thumb
would point down, and your fingers clockwise. Using the same
convention for twist ties is just a convenience, because it's the
way we expect to be able to open or close anything.

Incidentally, there are a few exceptions to this right hand rule.
The connections for fuel gas bottles are left handed (to avoid their
being confused with oxygen fittings, so you don't get an explosion
from mixing the fuel and oxidizer). Also, at one time the lug-nuts
on automobile wheels were left handed on the left side of the car so
that the forward rotation of the wheel would cause the lugs to
tighten, not loosen. There are also a few plumbing fittings that
are left-handed as well.