baldrick,

The spring in my Flues #3589XX has the spring inside the cocking plunger/Hook. A slot is cut in the Plunger to let the dog screw pass through to the spring recess and prevent rotation. The recess is 0.125" dia., the spring is 0.112" diameter. Grind 1/3 to 1/2 the dia. of a 0.125", or slightly smaller, drill bit shank to create a 1/8" long flat. Use it to compress the spring and install the dog screw until the screw is flush with the lug surface.

John