Originally Posted by
91MF
on a 107. if you put it on a 103 the outside is 42.
Wrong.
http://www.suginoltd.co.jp/singlespeeder_e.html
It's 45mm with matching 103 bb. If you go this route, check out Sheldon Brown to see cog/hub configuration will give something close to a 45mm chainline in the rear. Or get a 107 bb and put the chainring on the inside of the spider to get a 42mm (or something close enough) chainline.