Posted on March 29, 2014March 29, 2014 by admin What is the round turnable thing under and close to flamer adjustment knob? This is the air shutter, to adjust fuel/air mixture ratio for blue flame. Post navigationPrevious post: Could you tell me how your units compare to commercial Chinese wok ranges with foot controlled output?Next post: Why would one need a PF 13L 160 but output over say a PF13L 70?