Have a 2×10 set up on my MTB using a Deore M615 chainset http://www.chainreactioncycles.com/shimano-deore-m615-10-speed-double-chainset/rp-prod108774#

Its got 40-28T on it but I want an easier ride so want to change them to 38-24T.

I’ve bought 2 chainrings but not sure if they are the right ones!

38T says “HG-X CHAIN ONLY – 38-24 AM” pretty sure this is the right one…

24T says “24-AE SG-X” and came with a small plastic ring…. will this one even fit?!

The 38T should be fine (HG-X means 10 speed) but the 24 might not for 2 reasons: It says SG-X which means 9 speed so it might have different shift ramps tht don’t match up to your 38T and secondly 24 to 38 is a heck of a jump. The old SLX 2×9 was 36 and 26 if I remember rightly and that was a good old clunk.

Also make sure you have a 104 bcd large ring and 64 bcd small ring for those cranks. Some of the XT double sets are not the same BCD.

You can buy the M615 in 38-24T (on the CRC link above) so figured it must work if they sell them in that combination.

They were sold as a 104 and 64 BCD but should check TBH!

Oh and having had another look at the 24T its also got 10S stamped on it – so they obviously make SG-X for 10 speed too…… nice and straight forward 😐

Slx was 22/36. I know as I’ve just taken the rings off mine. 14 is the max jump for the front mech. I think you have to use 24&38 as the ramps on the 38 are spaced to match the 24. 24 granny will be the same wherever from as no shifting ramps needed. 9/10speed chain rings interchangeable.
I think what you’ve got should be fine.
Edit: am is right 38 ring for use with 24 granny:
http://www.chainreactioncycles.com/shimano-deore-fcm615-10-speed-double-chainrings/rp-prod133454?gs=1&gclid=Cj0KEQjwmKG5BRDv4YaE5t6oqf0BEiQAwqDNfDN386Op-oerVjVWDRfYUq_DJGZ9q1d9eaUdvHQXOqkaApIg8P8HAQ&gclsrc=aw.ds

Thanks docrobster – that was what my Google fu seemed to suggest.

Think I will just ignore the plastic ring (looks like the plastic bit in this picture)
http://i.ebayimg.com/00/s/MTA2NlgxNjAw/z/4gkAAOSwl9BWKziU/$_35.JPG

Edit: docrobster that is the 38T I have, but couldn’t find any specific 24T

sorry, don’t know where my head was and completely missed the 38-24 on your link and yes the SLX was 36-22.

The plastic ring is found on the low end chainsets (oem style below Deore), often with octalink BBs etc. Not idea what it’s for, maybe to stop the chain dropping into the gap between the crank arm and the BB bearings.

Thanks andyl – in that case the plastic ring is certainly getting ignored. When I get round to setting it up hopefully it will work perfectly!