Tension Washers are used in the construction of new plantation shutters where tension screws are incorporated into the panel.
In the diagram below a single Tension Washer is placed under the head of the Tension Screw in conjunction with the use of a Tension Bushing. The Tension Bushing was utilized in this depiction because a 1/4 inch diameter hole existed in the Stile. The Bushing was used to reduce the diameter of the hole and support the Tension Screw in the center of the hole. If your Stile hole was drilled specifically to support the Tension Screw, then a Tension Washer would be placed on the screw between the end of the Louver and Stile.
Tension Washers are made of nylon which has a low friction coefficient resulting in smooth action of louver(s).