The Transformation Cog, also refered to as a Transforming cog, transition cog, conversion cog, or T-cog for short, is an important component that is vital to a Cybertronian's transformation and sometimes, scanning. It enables the Transformer to scan alternate modes, transform and operate integrate transformable weapons systems inside of it. This component is in both male and female Cybertronians, and also in Predacons.
Without the T-cog, a Cybertronian loses into its alt-mode and operate its integrated weapons systems that require any reconfiguration of limbs. Transformer organs such as these are beyond anything to construct or repair according to Ratchet. Though Ratchet was able to repair Bumblebee's t-cog after it was badly damaged by Starscream.
All T-cogs are based on the original Transformation Cog possessed by Amalgamous Prime, the first Shifter and a member of the Thirteen. Amalgamous' T-cog apparently allowed him to constantly shift from one form to another, exceeding the abilities of his descendants. Other Cybertronians were not initially known to possess T-cogs, something that was discovered by the Quintessons and used to manipulate the early Cybertonians. It was only when resistance forces under Sentinel Zeta Prime examined Silverbolt immediately followed his emergence from the Well of Allsparks and discovered his T-cog in place that all of Cybertron became aware that the T-cogs were not in fact a Quintesson gift.