whats the frame made of?

i recently built an old, ancient MTB frame(old mariushi) into a commuter from my box of spare parts. the frame was meant to take a 6sp hub, all i had was a 7sp wheel to put on there(which is 4mm wider than the 6sp one). but since its a cromo frame, stretching it out that extra 4mm was no problem.....its just harder to take the wheel off and put it back on now. i would assume bringing the chainstays in 5mm would be fine too, unless its an alu frame...then forget it.

but if you wnat to ensure ease of opration, with a smaller hub id just swap out the axle and use spacers.