My router takes bits with 1/2" shaft size, and it came with an adapter sleeve that lets me use bits with 1/4" shaft. This sleeve is about an inch long and has a slit up the side.
Naturally at some point I broke this sleeve, but I still kept using it as long as I kept track of the parts, which I know seemed to have lost.
But I can't find anyone that sells this sleeve. Is it just me, or is this a hard-to-get item?