Cliff Rubber Gaskets & Brass Spacers for XLR & XLR Shell Feedthrough Connectors - Cliff CP299907, This red rubber gasket can be used both as a dust seal and for colour-coding an XLR shaped connector.
It can be used with or without the brass spacers supplied.
Cliff CP299907 Rubber Gaskets with Brass Spacers for XLR Connectors Red