Sinew Coils

The Sinew Coils, also called The Steel Within, is one of the twenty-two gene-seed implant organs of the Adeptus Astartes, and one of the three unique to the Primaris Space Marines. A Primaris Space Marine's sinews are reinforced with durametallic coil-cables that can contract with incredible force, magnifying his strength as well as giving his body another layer of defence. A Primaris Space Marine can crush a man's skull in his hand, break Flak Armour to flinders, or even bite through a metal cable should the need arise.