Message from discussion Traps: 38mm vs 76mm

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From: mike <miken...@yahoo.com>
Newsgroups: uk.d-i-y
Subject: Traps: 38mm vs 76mm
Date: Fri, 3 Jul 2009 11:12:27 -0700 (PDT)
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Are there any situations where it's acceptable to use a bottle trap
with a 38mm seal on a kitchen sink or do Building Regs always require
a 76mm seal?

Also, what's a "half trap"?

http://www.toolstation.com/shop/Plumbing/Traps+Waste/Appliance+Half+Trap+76mm+Seal+40mm/d20/sd2907/p52069

Isn't it either a trap or just a bit of pipe?