On Friday, July 6, 2018 at 3:16:27 PM UTC-5, Emanuel Berg wrote:
Ventura [1] has single speed chains that are
1/2x1/8", but also 1/2x3/32".

If there isn't a marking, can you deduct the
chain size from the width of the chainring
and/or sprocket?

Probably either chain will work, right?

$ echo $(( 1/8.0 ))
0.125
$ echo $(( 3/32.0 ))
0.09375

[1] http://www.ventura-parts.com

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underground experts united
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1/8 inch 3.2 mm is fixed / freewheel single speed only.
3/32 inch 2.4 mm is derailuer wheel inside width. Some fixed / freewheel also use this size to allow switching.

OUTSIDE width needs to be determined since it varies for each 6 to 11 gears.
https://en.wikipedia.org/wiki/Bicycle_chain#Width