Tread

Prompt and DeviantArt link for the 20th.

In the 200 year span between the 21st and the 23rd centuries, two things remained constant with all of the technological changes in military hardware: 1. All hardware used by the military is made the lowest bidder, and 2. The tread of combat boots remain the weakest point of the ground troops issued equipment.

For some reason, boots are built according to a milspec that requires them to last for years at a time. However, the same milspec leaves a lot of manufacturer judgement as to the lifespan of the tread on those very same boots.