Can Long Alloy Socket Set Screws Be Used as Threaded Studs?
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Fastener manufactures are being called upon to educate end users and distributors regarding fasteners to consider before purchasing, since, most often, the cost of fasteners is minor in relation to the cost of an entire assembly. This cannot be emphasized strongly enough, especially for socket set screws. The decision to purchase a socket set screw should be based on its designed purpose.
Socket set screws were not designed to be used as a threaded stud. Socket set screws are designed to hold parts together in a compression force and keep them from coming loose. Reference ASTM F912. A typical application involves holding a collar on a shaft.
Socket set screws should not be used in a tensile application as threaded stud without much consideration to lowering the hardness. If a set screw(s) fails, damage to expensive equipment could occur, not to mention downtime, production losses and possible injury.
Can Long Alloy Socket Set Screws Be Used as Threaded Studs?
Alloy socket set screws are widely recognized for their exceptional strength, hardness, and wear resistance. Manufactured to a typical hardness range of Rockwell (HRC) 45-53, these fasteners are designed for compression applications. For example, locking, positioning, and transmitting force against another component. However, a common engineering question is whether an alloy socket set screw can also be used as a threaded stud.
The Answer
It is NOT RECOMMENDED. It comes with a VERY HIGH RISK, LIMITATIONS and PRECAUTIONS if the hardness is not lowered. While alloy socket set screws possess high tensile strength, their hardness also introduces characteristics that must be carefully considered during design and installation.
Should You Consider a Long Socket Set Screw for Use as a Stud?
In certain applications, engineers use threaded studs to provide:
- Permanent thread engagement in a housing
- Improved serviceability
- Increased thread engagement
Since socket set screws are manufactured from high strength alloy steel with a standard hardness of RIC 45-53 and are fully threaded, they may appear to be an attractive substitute for conventional threaded studs. This certainly would create a very high-risk situation. If used with the standard hardness.
Understanding Material Properties
The hardness specification for socket set screws is HRC 45-53 and provides several advantages:
- High tensile
- Excellent wear resistance
- Resistance to thread deformation
- Good fatigue performance under proper loading
IMPORTANT: Increased hardness also results in reduced ductility. Unlike softer steels such as threaded rod with a hardness range of HRC 22-35 can deform slightly before failure. Hardened alloy set screws are much less forgiving when subjected to shear, excessive bending, impact, improper installation.
Precautions: Using a Socket Set Screw with a Hardness of RIC 45-53 as a Stud is Not Recommended
1. Avoid Excessive Installation Torque
One of the most important considerations is installation torque. Because the socket set screw hardness is significantly harder than many of the materials into which it is threaded, excessive torque can:
- Damage mating threads
- Strip softer parent materials
- Cause thread galling if stainless mating materials are involved
- Introduces unnecessary tensile stress
2. Consider the Mating Material
The hardness difference between the set screw and the mating material is critical.
For softer materials such as:
- Aluminum
- Brass
- Cast iron
- Low-carbon steel
The hardened threads may act like a cutting tool if over tightened. Providing adequate thread engagement and following recommended torque values helps prevent thread damage.
3. Minimize Bending Loads
Socket set screws are designed primarily for axial loading or compression applications. When a long socket screw is used as a threaded stud, the design should ensure that:
- No side loading without considering hardness.
- Misalignment does not introduce bending stresses.
Because of their high hardness, alloy socket set screws may fracture if subjected to adverse tensile condition repeated bending, impact loading, side loading or used in any way that may cause undue stress.
4. Prevent Hydrogen Embrittlement
If the set screw has been electroplated, verify that proper post-plating hydrogen relief baking has been performed. High-strength alloy fasteners are susceptible to hydrogen embrittlement, which can lead to delayed brittle failure under sustained tensile loads.
Many applications avoid this concern by using black oxide or phosphate finishes rather than electroplated coatings.
5. Use Proper Thread Engagement
As with any stud installation, sufficient thread engagement is essential.
General guidelines include:
- Steel components: engagement approximately equal to 1.0 to 1.5 times the screw diameter.
- Aluminum or softer alloys: 1.5 to 2 times the screw diameter or more, depending on material strength.
Adequate engagement distributes the load across multiple threads and reduces the risk of thread stripping.
Are They as Strong as Conventional Studs?
In many cases, alloy socket set screw equals or exceeds the tensile strength of standard steel studs. However, conventional studs are specifically engineered for tensile loading and often include controlled material properties and hardness that optimize both strength and toughness.
Socket set screws should be viewed with caution as a practical substitute only when the application does not require bending resistance, repeated impact loading, or specialized stud features.
Typical Applications
Using alloy socket set screws can be appropriate in applications such as:
- Fixture assemblies
- Machine tooling
- Bearing retainers
- Precision mechanical equipment
- Jigs and gages
They are not suitable for:
- Structural joints
- Heavy fatigue applications
- High-impact machinery
- High stress applications
Conclusion
Alloy socket set screws can successfully serve as threaded studs when the application is properly engineered. Their high hardness of Rockwell C 45-53 provides excellent strength and wear resistance, making them well suited for many industrial and machinery applications.
However, the same hardness that provides these benefits also reduces ductility. Engineers should always consider lowering the hardness of the socket set screw before using it in their application to avoid any major problems. Always ensure that the socket depth is kept out of tensile, adequate thread engagement and consider the strength of the mating material. When these precautions are observed, alloy socket set screws may provide a durable, high-strength alternative to conventional studs in many non-structural applications.