The Fin Drive replacement fins are manufactured from very durable rubber. Tapering off from the front to the back to mimic a fish swimming action the fins provide maximum propulsion whilst still maintaining a stealth approach. There is a brass adjustment knob that attaches to a stainless steel ring for easy securing. There is also spacing for a stainless steel 33cm bar to be inserted into the fin to give it the stiffness it needs to perform at its best. The 33cm Stainless bar is not included with the fin replacement.