To fit a disc brake on a #600 Schlumpf hub, you’ll need either to sand down the frame or use spacers. The second solution is rarely the one that is used as the spacers have to endure a lot of stress so they tend to break.
If you want to run a disc brake on a Schlumpf hub without any modification, you need at least a #800. Please see this topic to know more about changes from a hub generation and the next one.
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