The Hidden Risk of Fasteners - Why 3A Threads Matter

Thread class is a critical specification that defines how tightly a threaded component fits with its mating part. A Class 3A thread provides a more secure connection—it’s the standard for hex socket set screws. However, the folks at Screw & Mfg. Co. have recently observed the misuse of Class 2A threads where a Class 3A is required. This isn’t just a minor detail; it’s a serious quality risk that can compromise the integrity, fit, and function of a mechanical system. 

In firearms, archery, and precision equipment, small details separate reliable performance from failure. A 3A thread fits snugly into a 3B hole, providing a close, precise fit with minimal clearance. That tighter tolerance keeps adjustment screws locked in place under recoil, shock, and vibration, ensuring superior alignment and long-term durability. Critical applications include AR-15/M5 lower receiver (nylon tip adjusting screw); iron sight leveling screw; trigger over travel screw; quiver, rest, and sight mounted to a bow; and scope rings, mounts, and bases.

By using 3A threads where they are specified, you're not just following a rule; you're building a stronger, safer, and more reliable product from the ground up.
“At Set Screw & Mfg. Co., we’ve been in this industry since my grandfather supplied gun parts during World War II,” says fastener specialist Heather Walker. “We are ISO 9001:2015 certified, and every order is inspected before it ships. Because in this field—and for our armed forces—‘good enough’ isn’t.’”

Founded in 1935 in the basement of Calvin O. Brown’s home, Set Screw & Mfg. Co. is now led by his son Jim Brown from a 30,000-square-foot manufacturing facility in Elgin, Illinois. With 46 Brown & Sharpe machines, four thread rollers, a full line of tip machines, and nearly 90 years of experience, and fourth generation ownership, the company stocks over 10,000 sizes and styles of set screws ready for immediate shipment in steel, stainless, brass, bronze, aluminum, and specialty materials.

Every detail matters—and the IFI (Industrial Fasteners Institute) standard exists for a reason: If a design calls for a 3A thread, you must use a 3A part. Hex Socket Set Screws are 3A, no exceptions.

To ensure compliance, Set Screw & Mfg. Co. verifies thread class on all nylon and brass tip set screws before every shipment, confirming full 3A IFI conformance.