Possibly stupid stem question...

So my fixed conversion is an old Dawes Jaguar. I'm mucking around with stems and have found that it seems to take a much smaller than 1" variety. The steerer tube internal diameter is 18mm. According to Sheldon, this doesn't exist. Anybody throw me a line here?

1) keep checking ebay for old stems, something will come up! ( eventually)
2) new forks if they fit in the headtube
3) possibly find a quill to head converter that will fit you 18mm dia.

sorry not much help

18mm is a bit odd. Are you sure? In the late eighties some 'bikes' came with BMX sized 21mm stems. If you want one that size I have one you can have.

Pretty positive. I must be measuring something wrong or it's the failing battery in my calipers. I have two stems that fit (an old Salsa one and a no-name one that came with some bars I bought from Henry) and two now that don't fit. The two that don't fit are definitely standard 1" quills and the others are quite clearly smaller.

18mm ? 18mm should look noticeably slimmer. I have french stems that are stamped 21.9 but that is a big diff from 18.
use the calipers and put them up to a ruler. see if its 18mm.

18mm ? 18mm should look noticeably slimmer.

It does. Fresh battery going in the calipers this evening and I'll measure again.

Joke's on me. Fresh battery in my calipers and it now measures as a standard 1". Compounded by the fact that I thought I had a 1" quill-to-ahead adapter in my hand when it was actually a 1-1/8" one.