On Mon, 10 Dec 2007 14:25:37 -0800 (PST), Rupert Candy
wrote:

On Dec 10, 10:15 pm, "Jonathan Morton"
wrote:

The 317s were very advanced trains for their time. They were the first
trains to have retention bogs, for the underground section to Moorgate [1].
[1] I believe some genius actually removed these later.

That's the first time I've heard that - is it definitely true?

You are correct about the 313s - they are the only stock cleared for this
line, because the loading gauge is tube-size - or only slightly bigger.

Quite a lot bigger than tube (or Tube) gauge, though you're right that
not all standard EMUs would fit through the tunnel. 313s are at least
as big as LU sub-surface stock though...

They aren't. LU sub-surface stock is out of gauge sideways when
running on NR lines not cleared for their passage; c313 bodies also
have a taper toward the top so that if the air-bag suspension fails
catastrophically on one side the top of the carriage does not lean out
of gauge. You'll notice the difference especially if you change from
one to the other and use the window seats.