I need to change the gear cable outer on a bike I bought that has XTR shifter and RM.

It seems the outer on the bike is significantly bigger diameter (I’d say 6mm) then the little loop I have in my stores (which is about 4mm).

Does it matter if I use the 4mm and do I need special larger ferrules to make the difference at the shifter/RM interfaces?

Ta.

If you measure the internal size it should be the same, I’m pretty sure it’s just there is more material to the XTR outer. The hole through the middle will be the same, gear cables are a standard size. I’ve never used anything special (and neither has anyone I know) with XTR stuff.

Thx Daniel, that makes sense for sure. Not clear tho how I secure the 4mm cable/ferrule in the slots on the RM and shifter that look designed to accommodate something larger. Does it ‘just work’ despite a bit of wiggle space?

It will just ‘work’ as long as you use the right ferrules.
Gear outer comes in two sizes: 4 & 5mm. If it is 6, then it’s brake outer not gear.
Usually the ferrules for 4mm are plastic & metal for 5&6mm.
Inner cables are all 1.2mm for Shimano but 1.1mm for some Sram, although they will work with each other without problem.
XTR is no different, just a special grease in the outer & sometimes coated inners.

Thx, I’ll have a go. It may be 5mm installed, am just measuring by eye.

Does it ‘just work’ despite a bit of wiggle space?

Yup, plenty of tension once the cable is through and tighten up, it won’t be going anywhere.

As for the XTR shifter, I’ve never had one before, I’m hooked. Damn another expensive MTB habit!

Heh, they do feel nice. My budget doesn’t go past XT unfortunately but I’ve done plenty of work on friends bikes with XTR on. Really nice stuff.

Im being dim here, but what’s RM refer to?

Rear Mech.