You could use the D-Brat from Daz freebie archive as a mechanical metal hand. There once was a Vue metal claw hand/arm but it's not in the freebies anymore. Mock has a freebie 2 finger claw robot arm thing in freebies here. haven't seen anything else around, just textures for various Daz models for more robot/tech feel of the regular hands. You may want to hunt down the terminator t-800 model by questor (I think?) and turn everything off but the arm. that would give you a good mechanical hand, robot piston feel.