Make your self a shim or have one made if you don't know how. With a bit of searching you should be able to find a metal super market in your neighborhood or shop online at McMaster Carr.
Originally Posted by
Robbs
Hi! I'm restoring my first project bicycle, a mid-80's Nishiki Sport, and fitting it with some new components. One of which is the threaded to threadless stem adapter. The bike uses a bunch of French-esque measurements that are pretty out dated, so it's difficult to find the parts that I need. The current stem is 21.8mm, I had a 1" stem, which won't work (obviously), but I purchased a 21.1mm thinking it wouldn't make a difference - asking the vendor if it would fit without a problem. I trusted it, but the .7mm definitely makes a difference - I can't keep the bars tight at all.
What are my options? I haven't been able to locate a 21.8mm stem adapter, does anyone know where I could find one? Would a different fork be in order to fit more modernized parts?