Knuckle-spikes

Knuckle-spikes are weapons used by the Autobot leader, Optimus Prime. They retract into his forearms when unneeded and are made from Cybertonium.

Fiction

Dark of the Moon film

During the battle at Chicago, Optimus used these to weaken the Decepticon known as Shockwave by punching him through the abdomen, causing serious damage. Optimus was able to finish him off from there. Dark of the Moon