If you want to keep foldabiliy you have to stick to the stock bars and stem. The stem diameter is common but not the clamp diameter and the handlebar. AFAIK, there are three different stock handlebars. The one piece, stem and bar do not separate, two, the S type bar sort of like brompton, and three the chopper style as pictured on wahoonc near the top of the thread. I think the third type is highest. I have heard of people undoing the wire loop curl and gaining a half an inch or so. That is the wire that loops around the brake bolt and limits you from having too little stem set in the tube.