Why?
Now got two NW chainrings that do not fit new chainring.
I guess I have to rummage around for an older chainset.

Because standards, why should you be able to buy anything with backwards compatibility? That would be far to simple.

That’s the M672 – specifically for 22/30/40 rings rather than 24/32/42 (M670) or doubles M675.

The M670/675 both run 104BCD, but to allow 30T middle rings, the BCD on the M672 is smaller.

Similar options for XT and Deore.

As above, its so you can run a 30t middle ring.

Its a pita when you have no idea as they look similar and you think you can just use your old ring etc…

Blackspire and works components make a n/w ring to fit, @£30 it may be cheaper than a chainset.

Thanks – stuck an old XT on.