Da - just thought of the reason - we all had it right - but think:

If the bottle is high pressured - and you un-screw it - you want to
vent the gas and liquid without blowing the top into someones eye
or the like. e.g. wet hands but not broken eye cornea.

Martin

engineman wrote:
On Mar 22, 9:00�am, F. George McDuffee gmcduf...@mcduffee-
associates.us wrote:
On Sat, 21 Mar 2009 22:28:21 -0700 (PDT), engineman

wrote:
I have a plastic bottle that once held Lipton's green tea.
when I looked at the threads on the bottle it looks like they consist
of segments.
The cap has similar threads.
I'm wondering what the reason for these strange threads?
Engineman
http://www.photoworks.com/photo-shar...sionid=7ED5DB6...
==========
Mainly so the parts can be molded without the need for a special
"unscrewing" core. �

By segmenting the threads it is possible to greatly simplify the
mold construction. �It also eliminates the parting line problem
on the threads where the mold closes greatly reducing
maintenance.

Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).

I sent the wrong link- sorry, here's the right one:
http://www.photoworks.com/members/engineman

I don't think that these threads were designed for pressure relief,
they seem to be very strong.
The bottle seems to have 3 parting lines and the parting lines are all
on the lands of the thread.
Also it appears that the length and positioning of the lands would not
permit removal of the thread from the mold without unscrewing.
Engineman