it's suppossed to be a 15mm hex wrench size, nut,
and when it is, there's room for a box wrench to go around it.

sometimes people put a 17mm hex nut there instead.
a box wrench may not fit around that size nut.

I'd say you are down to ..
vice grips,
heat it in place,
or unscrew it with a large semi-blunt cold chisel.

----- Original Message -----
From: "Danny Bean" <dannybean@ME.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, September 17, 2010 3:03 PM
Subject: Starter removal

> I'm currently removing my bad starter to install a reman one. The problem
> that I'm having is with the lower mount nut. Its on there and I mean on
> there. The trouble is the clearance between the but and the starter. Has
> anyone had trouble with this before and if so what do you suggest to get
> this stupid nut loosened and off. Btw its pretty rounded off now.
>
> Daniel Bean
> 615.973.4942