Sometimes it is hard to get a road shape bar through a stem, especially if putting a 26.4 in a 25.4, etc. For that reason, I keep short straight sections of bars that I've cut out of old and worn bars for this purpose. So I have 10cm sections of 26.0, 26.4, 31.8. Also works well for figuring out if some old mounting clamp is going to fit without scratching up a nice bar.