What size chain for 200gs FC-M202? This FC-M202 200gs has a label saying For NARROW chain only:



So what size exactly? Wikipedia lists three sizes:


3⁄32 in (2.4 mm),
1⁄8 in (3.2 mm), 
5⁄32 in (4.0 mm), or 
3⁄16 in (4.8 mm)


I can't find much information about the FC-M202 (is that because it is a very old crankset?), but this thread, Very Old Shimano 7 speed replacement mentions Shimano IG chain, and this question, KMC Z8S IG or HG compatibility, states that IG chains are not a good idea (as they are hard to find and can't be used with HG cassettes), and SRAM would be better.

FWIW, I currently have a FC-TY33, and the FC-M202 has the same gear ratios (48/38/28). I am not sure what chain I currently have (IG, HG or SRAM) - I have had a close look at it and there appears to be an italic 'I' stamped into each link, but my eyes could be fooling me (and TAIWAN stamped on the rear side of some of the links). 

However, it certainly does not look like this (nor does it have Shimano written on it):



The chain would have been purchased circa 2005, maybe.

I have an FD-M735 and a RD-M735.

My rear sockets are 28/24/21/19/17/14/12/11 (I think, I may have miscounted slightly), so 8 gears, but only seven of which are accessible.
Narrow means whatever was derailleur chain at the time, as opposed to wider singlespeed chain. The actual chain type is determined by the cassette and is very probably 7-speed.

The inch designations listed on Wikipedia are not commonly used except to distinguish between 1/8" singlespeed chain and narrower derailleur chains that are all lumped under 3/32" and distinguished by number of speeds in cassette. Note that on Wikipedia 7.1mm and 7.3mm both become 9/32".