Sidelock

Sidelock is the combined form of Sideswipe and Grimlock.

"Out of the Shadows"
While attempting to fathom the mysteries of how the Bee Team was able to combine into Ultra Bee, Fixit's explosive combination experiments caused Sideswipe and Grimlock to merge into a single bot, with Sideswipe's upper body and Grimlock's lower. Neither was very amused by the experience, which wore off fairly quickly, allowing them to join the rest of the team in pursuit of Shadow Raker.