apparently an inch across
they're weird though, sometimes they're proper nipples, sometimes they're more like a boil or something, with no defined sticky out bit
( weaver., Sat 4 Jul 2009, 1:09, archived)

yay!
it worked at last
( weaver., Sat 4 Jul 2009, 1:10, archived)

TMI
FREAK
( weaver., Sat 4 Jul 2009, 1:10, archived)