The 4RX1-2SS (also written as 4X1/2-A-TR-PH-SS) is a #4 size truss-head self-tapping sheet metal screw used in light aircraft, aviation assemblies, and general sheet metal fastening applications. It is designed to cut or form its own threads in pre-drilled holes in thin metal or similar materials.

This screw is commonly specified in aviation hardware catalogs and is used where a wide bearing surface (truss head) is needed to distribute load and reduce pull-through in thin materials.

Key features include:

#4 diameter sheet metal screw
1/2 inch nominal length
Type A self-tapping point (sharp tip for thin metal)
Truss head for wide load distribution
Phillips drive (PH) for standard installation
Stainless steel or corrosion-resistant steel variants (SS version)
Designed for sheet metal, aircraft skins, brackets, and lightweight structures
Suitable for vibration-prone environments when properly torqued
Common in aviation maintenance and fabrication work