To be honest, I found the inlets to be a definite choke point. The more I worked with them, the more I realized how much they pinch down as the air goes in and how irregular the first 3"/75mm.   If the inlet started at 39mm, it must have pinched down to 35mm inside necessitating a lot of prying and shaping with glass mandrel #1 (EvilTwinBrewing YIN Imperial Taiji Stout) with final shaping and polishing with mandrel #2 (Austria's Hofstetten Granitbock). While mandrel #3 (Oregon's RogueXS Bitter
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