I have the ES30G pipe. When I measure from the front edge of the pipe to the baffle, I get 16-1/2" approx. OR 18". I found that if you use a piece of 1/4" square balsa to stick down the pipe it will go down farther and therefore the 18" dim. I first used a 3/8" square piece of balsa and came up with the 16-1/2 dim. So depending what dia. you stick down the pipe, willl get you an 1-1/2" different dimension. Seems to be two baffles in the pipe. Also my Macs OS 140 header is 7-15/16" from the flange face to the end of the header. Hope this helps Rick.