Complex sentence: On 35mm film canisters there are two rows of six rectangular areas, the two left-most areas (with the spool post on the left) are both common-ground and are thus always bare metal.
Split into simpler sentences: On 35mm film canisters there are two rows of six rectangular areas. The two left-most areas (with the spool post on the left) are both common-ground and are thus always bare metal.