Every element of Kuzma's tonearm designs takes rigidity and energy transfer into consideration, so it should come as no surprise that this applies to their headshells.
In the photo (click to expand), take note of the longitudinal reinforcing ribs.
While they add rigidity, the narrow spacing presents a minor challenge, if you want to place washers underneath the mounting screws.
It's a minor point, but washers present a smoother surface for sliding the cartridge when making make fine adjustments during setup.
While the correct diameter washers are too wide to fit in the channels between the reinforcing ribs, the solution is simple: file flat spots on the washers.
The easiest way to do this is to hold the washer in either a bench top vice or a pair of Vice Grip pliers.
Simple ... no?
There's much to be said about washers, but in my experience, I've found brass and stainless to be my preferred materials.
I've seen many who advocate compliant materials like Teflon, Nylon and such. I've found that these softer washers tend to compromise the energy transfer between the cartridge and the headshell. This translates to blurred transients.
Suffice to say, that if you use washers, pay attention to their material and see what works for you, in your system. Some tonearm designs may have a different approach to energy management.