In my experience, Hardware Engineers determine clamping force needed, assess any creep and/or stress issues due to forces acting on the clamped joint including extreme heat cycles, and specify and/or design "Hardware" and specify number of fasteners and the fastener torque to meet the design criteria.
Whe I worked at the DOE where we processed nuclear waste, I helped an Engineer with some design concepts of a special bolt/nut concept that would equalize the stress along all the threads in the axial length. Typically, the first few threads in a nut and the corresponding threads in the bolt closest to the surface being clamped have much higher stress than the threads farther away. Due to the extreme thermal cycles and continuous heat of these units it was calculated that the bolts were going to stretch (creep) over the lifespan of the unit, lowering the clamping force and possibly allowing dangerous nuclear waste to spill in the cell. The extremely critical nature of these bolts required some really interesting ideas to egualize the stress on the threads to help eliminate this.
So, in a nutshell, "Hardware" to me means fasteners.
I think the term you're looking for may be "mechanical engineer".
I also think that the (UK) Institution of Mechanical Engineers (IMechE) summed it up nicely some years, in promotional material that simply said "Nothing moves without mechanical engineers."
Other major engineering 'fields' or disciplines would include: