Shoulder Section Can Serve as a Pivot Shaft
The smooth cylindrical shoulder can serve as a pivot shaft for rollers, linkages, gears, pulleys, or other moving components, allowing them to rotate around the shoulder section.
For mechanisms involving continuous rotation or high-speed motion, shoulder surface roughness, hardness, lubrication, and mating clearance should also be confirmed.
Provides Precise Positioning
The shoulder section can mate with component holes to control installation position, center distance, and direction of movement, making Shoulder Screws suitable for mechanisms requiring concentricity or repeatable positioning accuracy.
Actual positioning accuracy depends on shoulder diameter, hole diameter, tolerances, straightness, and assembly method.
Can Function as a Sliding Guide
Components can slide a limited distance along the shoulder section, making Shoulder Screws suitable for guide plates, sliders, linkages, and reciprocating mechanisms.
Lubrication, wear resistance, and surface treatment should be evaluated according to sliding frequency, load, and material combination.
Controls Spacing Between Components
The shoulder length can establish a fixed spacing between two components. After the screw is tightened, the moving component can retain sufficient rotational or sliding clearance rather than being clamped directly by the screw head.
Separates Fastening and Motion Functions
The threaded end provides fastening, while the shoulder section supports rotation, guiding, or positioning. This allows a single Shoulder Screw to perform both structural fastening and motion-support functions.
Supports Radial and Shear Loads
Compared with allowing lateral loads to act directly on a threaded section, the solid cylindrical shoulder provides a more continuous load-bearing cross-section and is better suited for radial or shear loads generated by linkages, moving components, and mechanical structures.
Actual load capacity should still be calculated and tested according to shoulder diameter, material, heat treatment, and load conditions.
Protects Mating Holes and Moving Components
Because the smooth shoulder has no thread crests, it can reduce scratching, wear, and binding that may occur when moving components rotate or slide directly against threaded surfaces.
May Reduce the Need for Separate Shaft Components
In certain mechanisms, a Shoulder Screw can replace a separate shaft, locating pin, sleeve, and fastening screw, helping reduce component count and assembly steps.
Whether these components can be combined should still be evaluated according to loading, safety factor, and maintenance requirements.
Precision Shoulder Diameter Improves Fit Stability
The shoulder can be machined or ground to control outside diameter, roundness, concentricity, and surface roughness, allowing it to work with bearings, bushings, or precision holes.
Compatible with Bearings and Bushings
The shoulder section can pass through ball bearings, plain bearings, bushings, spacers, or rollers to form a supporting shaft for moving assemblies.
When selecting a Shoulder Screw, confirm the fit tolerance between the shoulder diameter and bearing bore, and ensure that the shoulder length is sufficient to fully support the component.
Suitable for Compact Mechanical Designs
Because the shoulder, threaded section, and head are integrated into a single fastener, Shoulder Screws can reduce the space required for separate shafts and additional fastening components, making them suitable for compact machinery and electronic equipment.
Multiple Material and Heat-Treatment Options
Depending on shear strength, wear resistance, corrosion resistance, and operating environment, Shoulder Screws can be manufactured from alloy steel, carbon steel, stainless steel, or other materials, with heat treatments such as quenching, tempering, or carburizing.
Customization Based on Drawings and Samples
Shoulder Screws can be customized according to customer engineering drawings or physical samples, including head type, drive recess, shoulder diameter, shoulder length, stepped geometry, thread dimensions, overall length, end structure, material, hardness, tolerances, and surface treatment.
Common Applications
Shoulder Screws are commonly used in:
- Molds and stamping equipment
- Automation machinery and fixtures
- Linear guides, sliders, and guiding mechanisms
- Linkages and articulated mechanisms
- Rollers, pulleys, and gears
- Bearing and bushing assemblies
- Automotive and motorcycle components
- Electronic and electrical equipment
- Robotics and transmission mechanisms
- Packaging and conveying equipment
- Precision instruments and measuring equipment
- Moving joints and hardware for furniture
- Medical equipment and motion mechanisms
- Assemblies requiring positioning, rotation, sliding, or spacing control
Key Considerations When Selecting a Shoulder Screw
Before selection, first determine the actual function of the shoulder section, such as serving as a pivot shaft, sliding guide, locating feature, stop, or spacing element. Different functions require different specifications for shoulder diameter tolerance, surface roughness, hardness, and mating clearance.
The shoulder diameter should be selected according to the mating hole, bearing bore, or bushing inner diameter. Insufficient clearance may cause difficult assembly, rotational binding, or seizure after thermal expansion. Excessive clearance may result in looseness, runout, noise, or inadequate positioning accuracy.
The shoulder length should match the total thickness of the moving components plus the required operating clearance. If the shoulder is too short, tightening the screw may clamp the moving component and prevent rotation or sliding. If the shoulder is too long, excessive axial clearance or component movement may result.
A relief groove, fillet, or incomplete thread section may be present at the transition between the shoulder and the thread. Mating components and threaded holes should provide sufficient clearance to ensure that the shoulder can fully seat against the reference surface.
The threaded length should provide sufficient effective thread engagement for secure fastening but should not contact the bottom of a blind hole before tightening is complete. If the threaded end bottoms out first, proper clamping may not be achieved and the screw or workpiece may be damaged.
When the Shoulder Screw is subjected to radial loads, shear forces, or bending moments, the design should be evaluated according to shoulder diameter, material strength, unsupported span, and load direction. Overall load capacity should not be determined solely from the thread size.
If the shoulder section is used for continuous rotation or sliding, the material combination, lubrication method, surface hardness, and wear-resistant treatment between the shoulder and mating component should be evaluated to prevent long-term wear, increased clearance, or binding.
During installation, moving components should not be clamped directly between the screw head and the base. Before mass production, rotational resistance, sliding travel, tightening torque, shear strength, wear resistance, and fatigue performance can be tested to confirm that the dimensions and assembly conditions meet actual application requirements.
