Originally Posted by GCRyder
Your MTB shifters probably do NOT require bars as small as 22.2 (that's BMX size). Standard MTB bar size is 25.4mm, and there are decent, inexpensive drop bars also in that size. Most notably the SR Sakae bars that were OEM on tons of bikes during the 90s. About a half-dozen of those are on ebay as this is written.
Problem is he probably won't have much fun shifting, and the reach is probably all off. He needs bullhorns.