I am a paraplegic. I drive an adapted van with hand controls that include a Sure-Grip A600 spinner knob. This is equipment purchased from and installed by my mobility vehicle dealer, and is intended to allow operating the steering wheel with one hand so that the other can operate the throttle and brake, as well as other controls. Today while driving and making a hard turn, the plastic knob pulled off the shaft of the mount, causing me to lose control of the van and have a serious accident. This appears to be a clear case of defective product design as the plastic knob was merely pressed onto the shaft. The shaft and mount for it did not shift or move, but the knob pulled off. There were no features on the shaft to aid in retaining the knob beyond a friction fit.