Electro Hardware S521-M10-F21-H Round Circuit Board Spacer

Product Description

The ELECTRO HARDWARE S521-M10-F21-H is a round, female unthreaded circuit board spacer designed to maintain precise separation between a printed circuit board and a mounting surface or adjacent board. Manufactured from Grade 2 steel with a zinc-plated finish meeting ASTM B633 and QQ-S-633 Type 1 standards, this spacer provides corrosion resistance and dimensional consistency in electronic assembly applications. It accepts a No. 8 screw, measures 0.375 inches in overall length, with an inside diameter of 0.171 inches and an outside diameter of 0.25 inches. Electronics assemblers, control board technicians, and HVAC service professionals use these spacers when mounting or replacing control boards in equipment enclosures.

This spacer is suited for residential and light commercial electronic assembly work, including circuit board mounting in HVAC control panels, electrical enclosures, and industrial equipment. The female unthreaded design allows a No. 8 fastener to pass through while holding the board at a fixed standoff height. The zinc-plated steel construction makes it appropriate for indoor panel environments where moderate corrosion resistance is required. Sold individually, it is a direct drop-in replacement or supplemental fastener for standard No. 8 screw circuit board mounting applications.

Key Features

• Female unthreaded round body accepts No. 8 screw for straightforward board standoff mounting
• Grade 2 steel construction meets ASTM B633 and QQ-S-633 Type 1 finish standards
• Zinc-plated finish provides corrosion resistance for indoor panel and enclosure use
• Overall length of 0.375 inches with tight length tolerance of -0.005 to 0.005 inches for consistent board spacing
• Inside diameter of 0.171 inches with tolerance of 0.000 to 0.010 inches for reliable screw fit
• Outside diameter of 0.25 inches in a compact round profile for high-density board layouts

Compatibility

Designed as a standard OEM-style circuit board spacer for applications requiring a No. 8 screw, 0.375-inch standoff height, and a 0.25-inch outside diameter round profile in steel construction.

Installation Notes

Installation is performed by electronics assemblers or control board technicians. Always de-energize and discharge any capacitors in the control panel before handling circuit boards or fasteners. Use a standard No. 8 screw and appropriate hand tools; avoid over-torquing, which can deform the unthreaded spacer body. Follow applicable electrical codes and equipment manufacturer guidelines when replacing or mounting control boards.