I haven’t really likes the Middleburn outer ring I bought for my Shimano XT chainset so I’ve been looking at other options. TA seem to do some nice rings and do a 44tooth, 4 arm outer compact ring with a 104 PCD/BCD all of which match the my current Shimano outer ring. However, they also mention an 18mm arm width (I haven’t seen this with other rings), what does this refer to and as it’s a 4 arm ring with a 104mm BCD is it safe to assume that it’ll fit my Shimano chainset?

tick (as I’m not happy with Middleburn either)

arm widths come in either 18mm or 23mm I think, and is the width of the arm where it connects to the chainring. If you get one that is the wrong size, it will still work fine (I think), but it will look weird.

Well you say yourself, “it’s a 4 arm ring” – the arm is the bit that there’s four of, and the arm with is how wide those bits are. The implications are purely aesthetic.

Me type slow.