5 Things to Know When Buying Precision Shoulder Screws
Just as Dowel Pins and Retaining Rings are used to locate or hold parts together within a precision assembly or a fixture, so are Precision Shoulder Screws. Yet shoulder screws are far more versatile. When installed, the unthreaded shoulder acts as a shaft for rotating items such as bearings and bushings, precision spacing, machinery support, and motion guiding. The exacting tolerance of Precision Shoulder Screws makes them ideal for use with other precision components. They are broadly used across various applications in many industries, including: aerospace, electrical motors, hydraulic equipment, instrumentation, tooling and fixtures, machinery, military and many more.
Our goal is to make the buying process easier. This guide offers creative solutions to help you save money and reduce long lead times by educating you on your options, including how to use brand alternatives.
- What is a Precision Shoulder Screw?
Precision Shoulder Screws are generally classified as part of the electronic hardware family. They resemble socket cap screws with an enlarged, unthreaded cylindrical shoulder under the head, and are used to hold parts together within a precision assembly. Sometimes referred to as “tight tolerance” shoulder screws, they are not governed by any official ANSI or ASME standard.
Precision shoulder screws are composed of three main parts: the head, the shoulder and the thread.
- What materials and sizes are available?
Precision Shoulder Screws are readily available off the shelf in type 18-8/303 stainless steel and 416 stainless steel.
Standard stock sizes for the shoulder diameter are Inch from 1/8 to 1/2 and Metric from M4 to M12. The thread class is 2A and the tolerance on the shoulder diameter varies from +.000/-.001 to -.0005 to -.0015 depending upon the manufacturer. Now that’s precise!
316 stainless steel, alloy and other exotic materials, and special diameters and lengths are available in certain sizes and/or for special order and usually involve a lead time.
- What information do I need for ordering?
The easiest way to order is by manufacturer part number. If you don’t have one, you’ll need to specify shoulder diameter, shoulder length, thread size, material and drive type; for example: 3/16” shoulder diameter x 1” long x 8-32 thread in SS18-8 with a hex-socket drive.
Precision shoulder screws are available in hex socket and slotted drives. Philips, torx and star drives may be available in certain sizes as well.
Typical head styles are a modified fillister with a flat top where the head diameter is about twice the head height and does not need to be specified. Low head fillisters are available in certain sizes.
- Are there other factors to consider?
YES! One surefire way to save money and shorten delivery time is to cross the OEM brand part on your bill of materials to a functional equivalent.
Popular brands include: Amatom, Cambion, Concord, Globe, HH Smith, Keystone, Lyn-tron, Misumi, Pic Design, RAF, and WM Berg. A comprehensive selection of Precision Shoulder Screws is also offered by McMaster-Carr (tight tolerance series), MSC, and Grainger.
Let’s take the above example of a 3/16” shoulder diameter x 1” long x 8-32 thread in SS18-8 (300 Series) with a hex-socket drive. This part is offered by the seven brands (yes, seven!) listed below under the following part numbers:
- Grainger 6JY20
- Lyn-tron SS7431-00
- McMaster-Carr 94035A208
- MSC Industrial 67313726
- Pic Design 4423
- RAF 6931-SS
- WM Berg PZ-14-3
You can also find Precision Shoulder Screws under their Mil-Spec numbers, which include MS51575 and MS51576 and are DFARS compliant with full paperwork. The above part is equivalent to a Mil-Spec MS51576-14.
- What level of certification is required?
Generally, a Certificate of Conformance or a COC is sufficient for your customer. Full certification with material certs and test reports are often available for USA-made and Mil-Spec parts for a fee.
- The full range of commercial and Mil-Spec parts, including parts that are DFARS and ROHS compliant.
- Brand names and generic equivalents.
- Custom made parts per print in non-standard and exotic materials and finishes.
- Inch and metric sizes.
For more detailed information about Precision Shoulder Screws, visit our website. And if you don’t see it listed, as always, ask us. “Finding the right screw for you” is our tag line after all!
For more than 40 years, MF Supply has helped American manufacturers streamline operations, saving them time and money with our sourcing expertise and unique supply chain strategies. We are a WBE/WOSB certified stocking distributor of fasteners and electronic components.
We work with the best-established factories in the United States and DFARS-certified countries, and stock a huge inventory including all major brands and equivalents. MF Supply provides solutions including: same-day drop ship direct from the factory; custom sizes, materials and plating options; and DFARS parts with full paperwork and Certificates of Conformance.
We creatively solve common problems including hard-to-find parts and long lead times. Our sourcing and reworking expertise includes fast turnaround for modification of existing parts, hard to find standards and specials, special threads, non-standard diameters and lengths, exotic materials, special platings and short runs. We provide functional equivalents to expensive brand name fasteners and help our customers save money while reducing lead times.
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