I'm confused about this as well. Pen pressure is a dropdown option for a bunch of brush settings (opacity, flow, mix, wetness, size, roundness, angle, foreground/background, etc.). Which one are you referring to?
Looks awesome man, I might have to try this out. One thing that does look a little weird though, is in the example at the bottom it looks like the screw is part of the metal behind it... maybe you should add a little more of a shadow underneath it?
But who am I to tell you what to improve? That metal is spot on. Like I said before. Awesome.