I didn't give any thought to the plastic "tri-knobs" that hold the tension on the bimini when it's open, but I finally saw how little they work when I looked up and saw the bimini slightly flapping in the breeze. I figured that I just didn't tighten the adjustment knobs enough, so I tightened them a little more. An hour later, more flapping. When I took one off, I found that it was split up the side where the nut is inserted. Went to the hardware store and got some metal wing nuts to replace both of the plastic knobs. It will not slide lose, now. It also doesn't stand out like the black plastic knobs did.