The stoppers are all made with an end grained block of wood covered
with felt and leather. For the Soubasse pipes, I installed a blind t-nut in the block and used
a threaded rod to attach the stopper handle. The bottom surface of the stopper has to be hard and flat
so I plugged the hole for the t-nut.
I turned mahagony handles for the lowest 12 Soubasse pipes since they are part of the façade on the sides.
Here's the largest stopper for the Soubasse CCC pipe:
For the Bourdon stoppers, I just glued the handles to the blocks. I found some softer felt that worked
Here's the stopper for the smallest Bourdon pipe, A3: