Steel chainstays are fairly flexible, so they're generally a bit wider than the exact spacing: When you bolt the wheel on, they squeeze together against the spacers. It's possible to go the other way and squeeze in a slightly larger hub, or cold set (read: bend) the chainstays out to handle a much larger hub. There are a lot of people who do this to fit a modern 7/8 speed cassette hub in a nice vintage frame.

- 50% larger than Scrod