Air damper design

[newsite smokers]

I'm using a 4"round pipe. What's the best design for the cap/cover of the opening? Best to open/restrict air flow

 

[forktender]

A 1/2'' sleeve and a piece of 3/8" "All Thread"/ threaded rod, bent into and L with a piece of 1/4'' plate cut to the shape of the pipe then weld the L piece onto the plate and the sleeve onto the stack. Drop the L shaped A.T. through the sleeve and double nut it on the bottom to hold it in place so it won't come off. You can add a spring to the A.T. to keep a bit of tension on it when it's the closed off position.