How They’re Made
Precision shoulder screws are turned from bar using CNC machine tools that tightly control tolerances and dimensions. While most machine screws are cold forged from coil using cold heading equipment with rolled threads as a secondary process, U.S. Shoulder Screws feature cut threads specifically engineered for precision applications.
Cut Threads vs. Rolled Threads
Rolled threads tend to be stronger, because no material is removed when rolling the threads and the grain flows in the metal run in more than one direction. However, rolling threads results in diameter reduction. For example, on a 1” diameter bar, after rolling the major diameter of the threads is reduced to .912.”
Rolled threaded product is typically produced using a forging process, which overall is less precise as a manufacturing method than turning, and tooling costs are prohibitive for smaller production lot sizes.
Benefits of Cut Threads
Though more expensive to manufacture, cut threads are highly precise. Because parts are turned from bar, there are other benefits of the precision manufacturing attributed to cut threads, including:
- Undercuts beneath the head to ensure that the head can lay flush against a perfectly flat surface – which are common in tool and die designs.
- A precision shoulder that is undersized to the nominal size to provide a clearance fit when installed in a hole. The smooth shoulder acts as a pivot or bearing surface while minimizing wear and resistance from friction.
- A precision head that is carefully controlled for height and diameter. Other head features such as knurling for finger loosening and tightening can be done in a single manufacturing process, whereas with forging, such features must be completed as a secondary process.
- A drive system to enable torqued installation using tools. Standard drives are hex-socket. Six-lobe designs (Torx™ style) are available in limited supply from stock, but can be manufactured to order.