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The Shimano spokes are proprietary with flattened spoke heads, but I've been playing with some old C35 hubs and some straight pull CX-Ray spokes and they seem to fit fine. I can see that the flattened heads would be useful when you're building them in a production environment, as it'll stop the spokes twisting when you're building them up, but at the moment I can't see any reason why CX-Ray straight pull spokes shouldn't work. Haven't got round to actually using them in a new wheelset though, although I do have the rims I need to reuse them.
Brommers-
From the same thread from weight weenies:
Space could be tight.
Flattening your own spokes does not sound that difficult:
For example, it looks like the flattening isn't quite 2 mm across (the flats aren't quite even with the spoke diameter). Possibly it's around 3 mm or so. I would measuring to confirm, then maybe tape two 3 mm allen keys (or some other hard things which are the right thickness) in my vice and flatten each spoke head, with the allen keys functioning as a repeatable spacer or tooling stop.
So just squash them a bit in a vice...
https://weightweenies.starbike.com/forum/viewtopic.php?t=150872#p1389190
svenhöek
Thought they might be proprietary, shame as the hubs seem great...