259857 - Miller 3/8-16 x 0.87 Grade 5 Hex Head Screw, Black Plated

Engineering Grade Fastening for Industrial Equipment

The Miller 259857 Screw is a precision-engineered hardware component designed specifically for the assembly and maintenance of Miller Electric welding power sources and industrial machinery. Identified by the technical specification ".375-16X .87 HEX HD-PLN GR5 PLD BLK," this fastener represents a critical element in maintaining the structural integrity of heavy-duty equipment. The screw features a 0.375-inch (3/8") diameter with a Unified National Coarse (UNC) thread count of 16 threads per inch. This coarse thread profile is selected for its superior resistance to stripping and cross-threading, particularly in applications where frequent disassembly for maintenance may be required. The length of 0.87 inches (approximately 7/8 inch) is calculated to provide optimal thread engagement depth without protruding into sensitive internal clearance zones.

Manufactured to SAE Grade 5 standards, this fastener is constructed from medium carbon steel that has been quenched and tempered. Grade 5 hardware is significantly stronger than standard Grade 2 commercial bolts, offering a minimum yield strength of 92,000 psi and a tensile strength of 120,000 psi. This high strength-to-weight ratio is essential for welding machines that are subject to thermal expansion cycles and mechanical vibration during operation and transport. The use of Grade 5 hardware ensures that chassis panels, internal transformers, and mounting brackets remain securely fastened under load, preventing mechanical looseness that could lead to noise or component failure.

The "PLD BLK" designation refers to the fastener's black plated finish, typically a black zinc or black oxide coating. This surface treatment serves two primary functions: it provides a layer of corrosion protection against the humidity and atmospheric contaminants found in industrial welding environments, and it maintains the aesthetic continuity of the equipment's design. Unlike bright zinc or galvanized fasteners, the black finish blends seamlessly with the dark chassis components of Miller welders. Utilizing genuine OEM hardware like the Miller 259857 guarantees that the replacement part meets the exact metallurgical and dimensional specifications of the original engineering design, ensuring reliable performance and safety.