Thrust washers or thrust bearings are very important in gas model boating as well as necessary for most Enforcer drive systems. With a floating, or solder-less drive cable system using square ends such as ours, the forward thrust (motion) produces a great amount of pressure that bears down on the rear of the strut blade. A series of two to four thrust washers, or a thrust bearing set is installed between the drive hub and the rear of the strut blade or bearing housing. The forward pressure now causes the thrust washers or bearing to be sandwiched so to speak between the two surfaces keeping direct "rubbing" friction from the two metal surfaces.Without thrust washers or bearing sever damage would occur to the strut blade and drive hub. For sport performance (everyday) fun we only recommend the use of these innexpensive Nylon washers, as they are considered wear items that require more frequent replacement, and are more cost effective when using your boat for several hours a weekend. One of the best features of Nylon thrust washers is they tend to wear one at a time and can be replaced one at a time.