a clock case comprising a first plurality of upstanding , spaced - apart fins formed from flat sheets of material , each of the first plurality of fins having a plurality of slots extending vertically upward from a bottom edge ; and , a second plurality of upstanding , spaced - apart fins formed from flat sheets of material , each of the second plurality of fins having a plurality of slots extending vertically downwards from a top edge . each upwardly extending slot is configured to mate with a respective downwardly extending slot , whereby each of the first plurality of fins is interlocked with each of the second plurality of fins to form an orthogonal array of laterally extending fins and longitudinally extending fins .