From Teletraan I: The Transformers Wiki

A transformation cog, also referred to as a transforming cog, is an (apparently) important component for allowing a city-Transformer, such as Trypticon or Metroplex, to transform.

[edit] Fiction

[edit] Generation 1 cartoon

Metroplex's cog was damaged in 2005 during the Decepticon siege of Autobot City, which explains why he did not transform to robot mode during the battle. Perceptor built a replacement cog and entrusted its delivery from Cybertron to Autobot City on Earth to Blurr and Wheelie. This proves you can be brilliant but still stupid. Five Faces of Darkness, Part 1

After numerous setbacks, the cog was delivered just in time. As the city was under siege once again, Pipes quickly installed it, allowing Metroplex to fight off Trypticon. Five Faces of Darkness, Part 5

The cog also makes a nice substitute for a football. Apparently, it can also change its shape to look like flat, toothed wheel every time a lazy animator wishes it.

Unicron required Trypticon's cog as part of his scheme to use Cybertron as his new body. Ghost in the Machine

[edit] Beast Wars

Nitrostreak suffers from a broken transformation cog. Dawn of Future's Past

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