Page "Roller chain" Paragraph 7

If the chain is not being used for a high wear application ( for instance if it is just transmitting motion from a hand operated lever to a control shaft on a machine, or a sliding door on an oven ), then one of the simpler types of chain may still be used.

Conversely, where extra strength but the smooth drive of a smaller pitch is required, the chain may be " siamesed "; instead of just two rows of plates on the outer sides of the chain, there may be three (" duplex "), four (" triplex "), or more rows of plates running parallel, with bushings and rollers between each adjacent pair, and the same number of rows of teeth running in parallel on the sprockets to match.

Timing chains on automotive engines, for example, typically have multiple rows of plates called strands.