Closet door knob stiffener.

Used to keep closet knobs from rotating.

We had several closet doors installed that are hollow core. The knobs, properly installed, could not find adequate purchase on the door surface and would rotate. Tightening the screw hardware had little effect, and would warp the door. This is a first pass that works. I think the most important part of the design is the standoff section that pinches the standoff between the outside wall and the knob. My design probably has more features than needed. Like the inner plate that keeps the standoff from falling into the door, but first pass it worked great and I did not feel a need to tweek it other than add a fillet between the large plate and the standoff.