Review on Firestik SS 3H Stainless Antenna Spring by Carlos Jass

I attached them to a 2ft Fire-Stik on a Class 8 truck mirror. There's a bit of movement at highway speeds, but it doesn't rock. More like wobble. It would probably handle a 3ft firestick, but I don't know about longer ones. I tried the same antenna in "medium mode", the spring didn't have enough stiffness for the fireworks - the antenna dangled at highway speeds. I've attached a medium-strength spring to a lighter, two-foot smaller antenna on the other side of the truck and all is fine.