I've just got the bits together to go 2×9 – a 36t chainring and a double front mech.

When I've come to put everything together, the chainring has the correct BCD, but the mounting tabs are about 1mm too long, so it can't be bolted up. The tabs are the same size as the ones you get on a big ring, but this is definitely a middle ring.

The ring's a Deore M532 according to the packaging, whilst my cranks are Deore M540 (2005 or so). I've offered it up to an old Alivio crankset (2001 maybe?) and there's the same problem.

Is the M540 oddly sized? Is there an off the shelf chainring that will fit, or do I need to start filing down the 36T ring I have?

This does happen with some combos but I've not heard of it when mixing Shimano.

I'd just get the file out.

Yeah, a bodge is called for. I'm sure SLX are slightly oversized, so wouldn't surprise me if others were.

+1 n- as abover – file them down – did that on some inner rings for internal on and external BB cranksets 🙂 Or send em back I suppose?

You want M510 rather than M532 – they have normal sized tabs.

Either that or file them down.

File time then. Can't really be doing with sending them back and getting new ones from a different supplier etc.

A Shimano chainring is tougher than a dremel multi. I wouldn't advise anyone to try filing steel chainrings by hand!

I filed some down, well dremeled them works fine.