Original hardware on the left, my choice of hardware on the right.
View attachment 32794
View attachment 32795
Below, my hardware on the left, original on the right. I feel good about the aluminum washers against the kettle. Weber must do it for a reason. I believe the aluminum will conform the the slight curve of the bowl and the aluminum will protect the porcelain from the expansion/contration/flexing of the hard steel screws. I also think the washers give a higher standard of build appearance.
I chose slotted screws because that's what Weber has used in the past and I believe they will be easier to clean than other choices. Have fun digging a couple of years of hardened gunk out of that screw on the right.
You can see how close the grate is to the screw heads, that's why I put the nuts on the outside.
View attachment 32796