When replacing the black door handle w/ chrome ends on an old style K series smoker the new door handles use screws size 1/4-20.
You may have to drill out the hold on the back side of the door so the new screw heads can fit into the recessed hole to mount the new door handle.
On the new door handle one end is larger than the other, but there is no official top or bottom.
We always install with the larger end on the bottom, but it doesn't matter either way.