1

This FC-M202 200gs has a label saying For NARROW chain only:

Narrow chain only label

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):

IG51 chain

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.

2

If you have an 8 speed rear, you just need a derailleur 8 speed compatible chain. Chains are sold in 7 speed and below, 8, 9, 10, 11 (and 12) speed versions.

All derailleur chains are 3/32" / 2.4mm, which is the distance between the inner plates. 8, 9, 10, 11 speed chains all share that inside dimension, but have progressively narrower outside dimensions to accommodate more closely spaced cassette sprockets.

If your derailleur cannot shift onto all the sprockets you need to check the derailleur indexing and limit settings, then the function of the shifter, and the housing/cable run.

3

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".

  • To clarify: All derailleur chains are 3/32" / 2.4mm, which is the distance between the inner plates. 8, 9, 10, 11 speed chains all share that inside dimension, but have progressively narrower outside dimensions to accommodate more closely spaced cassette sprockets. – Argenti Apparatus Oct 3 '18 at 19:01
  • 1
    To confuse things even more, cogs get thinner with more cogs in cassette even if the internal chain width stays the same. And good luck trying to fix Wikipedia once wrong information is there... – ojs Oct 3 '18 at 19:36

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