bicycle chain width specs... ...

For inner chain width there are the following standard dimensions:

Single speed chains have inner width of 1/8″ (3.175 mm).
Multi speed chains, from 5 to 8 have inner width of 3/32″ (2.38 mm).
Multi speed chains from 9 to 12 speeds have inner width of 11/128″ (2.18 mm).
“Exotic” standard for freight bicycles is 5/32″ (4 mm).

Props to Bike Gremlin for this info!