Are narrow-wide single chainrings compatible between 9, 10, 11 and 12 speed? I am planning to convert my bike to 1x12 setup. Since it is an old bike I want to keep it as low budget as possible. I am looking to keep my existing BB an crank. I have read multiple posts about people just dropping high and low chainrings from 3x ring chainset and replacing middle ring with specific narrow-wide chainring suitable for 1x by setup. It does not look very slick, but there is no reason why it would not work.

So far so good. But now I am in the market for a narrow wide chainring. I can get BCD and number of tooth that I want, but some of these chainrings are advertised as 10speed compatible, others say 9x, 10x, 11x etc.

So the question is: what exactly is so specific in narrow-wide chainring that makes it compatible with say x10 but not x12? Any advice appreciated.
I would have thought that most narrow-wide rings would work with 9 through 12 speed chains. as they all have the same internal (roller) width.

Chains from 5 to 8 have an inner width of 3/32″ (2.38 mm), chains from 9 to 12 speeds have an inner width of 11/128″ (2.18 mm).

Looking at a Blackspire ring:


  For use with 9, 10, 11, or 12 speed drivetrains
  
  For 9 speed drivetrains you must use a 10 speed chain.


Same for Wolf Tooth:


  Compatible with all 10-, 11-, and 12-speed chains except Shimano 12-speed chains.
  
  If using a 9-speed drivetrain use a 10-speed chain( shifts and works well on a 9-speed drivetrain and fits the ring tighter for better chain retention)


They obviously think there is something about 9 speed chains that does not work with their rings as well as a 10 speed chain.