which slot to use

I want to build up a 35 pound kettlestack
which slot should I use ?

Since our new_handle_design

Since our new_handle_design has a slightly higher profile, you can use the higher slot (closer to the handle) for all setups that have a 5 lb plate in the core.

two 35 pound kettlestack kettlebells

Here's a picture of two typical two_35_pound_kettlestack_kettlebells: The left one using slightly thicker 5lb plates.