Speed Fastener U Nut Spire Clips Pack of 10 Screw Size Variations U Nuts / U Clips. Screw sizes: No. 4, 6, 8, 10, 12 & 14. U-Nuts provide a strong and secure fixing for applications where two or more panels require holding together. Typical applications include motor vehicles, domestic appliances, electrical equipment and machinery. Used on door trims, roof linings, interior door panels, dashboards etc. Information The TR U-nut is a fastener composed of two flaps in clip form with two external raised thread forms. The design of this nut means that a double elastic force is exerted when tightened. This nut can be held in place manually when tightening. No special tools are required to mount U-nuts, and they can be assembled much more quickly and easily than conventional nuts. The self-locking feature means that costly operations such as tapping, welding or riveting can be avoided. It can also be used with fragile materials such as glass, plastic or enameled surfaces. In these cases the resilience of the nut avoids cracks or damage to the application area. This nut locks with tightening torques much lower than for standard nuts due its great resilience. It is normally mounted on the edge of a panel but it can also be used in a rectangular mounting hole in the middle of a panel.