Thread InsertsThe 137M4 threaded insert is a brass insert produced by Tappex Thread Inserts with a part number of 37915. It is M4 in size, measuring 8.4 millimeters in length. This insert has been designed to provide a strong, corrosion-resistant thread for installation in a variety of materials, such as plastics, composites, and even light metals. TRISERT® inserts feature high strength, easy installation, and self-tapping threads for increased performance and accuracy. The insert is ideal for use in applications which require a lightweight, durable fastener.