8 Things to Know When Buying Set Screws
Our goal is to help simplify the buying process for this sometimes-complex category of fasteners by detailing the most critical things you must know when buying Set Screws.
- What is a Set Screw?
A Set Screw is a fully threaded headless screw that is traditionally classified within the socket family of products. It is generally used to fasten an object within or against another object by exerting pressure rather than holding parts together with threads. It is normally used without a nut.
- Who uses Set Screws?
Set Screws are used in many industrial and mechanical devices, particularly in assemblies with rotating items such as pulleys or wheels, where a component is locked onto a shaft. Designed to fasten one object inside another, Set Screws pass right through a threaded hole in the outer object and are tightened against the inner object. Pretty cool, right?
Check out this video for a demonstration of installation and application.
- What materials and platings are available?
The three most common Set Screw material options are alloy steel, stainless steel and brass.
The most commonly available material is hardened alloy steel with a thermal black oxide finish, as per ASME B18.3 and a Rockwell hardness of C45-53.
Stainless steel grades 18-8/303 and Metric A2 are also commonly available. Other exotic materials such as brass, 316 or A4 stainless steel, 4140 steel, 416, A286 or special finishes including zinc plating may be available for special order with a lead time.
Socket Set Screws come standard with 3A thread fit. Some sizes and materials may be available with nylon patches or pellets.
- What sizes are available?
In our experience, Set Screws are most commonly available in sizes 2-56 through 1″ in imperial and M2-M24 in metric diameters with a hex socket drive on one end and a cup point on the other.
- What information should I provide to get an accurate quote?
The easiest way to order is by part number. The most popular manufacturers of Set Screws are Holo-Krome, Blue Devil and Misumi, along with the national catalog houses like McMaster-Carr, Grainger and MSC Industrial.
If you don’t have a part number, you’ll need to provide the diameter and thread, the body length, drive and tip type, material and plating.
- Other than size, material and plating, what other options are available?
The other main considerations when selecting Set Screws are the drive and the point. We offer a comprehensive look at your options below.
The most common and readily available drive style is a hexagonal socket drive (think Allen wrench), however, Set Screws may also be available in slotted, six-lobe (Torx) and spline drives for certain sizes.
This is where it gets interesting. The point of the Set Screw determines its function. Seven (yes, seven!) main points are available, each serving a slightly different purpose.
Cup – The most common style, which is slightly cupped to meet the surface of the inner object. Used for permanent or semi-permanent installations, the Cup point provides a high level of security and control. (Metric DIN 916)
Knurled Cup – A variation of the Cup point, this style has knurls for a stronger grip.
Cone – A very sharp point wedges into the inner object to hold it permanently in place. With the highest holding power of all Set Screw styles, the Cone point is used for permanent settings. Note: Cone point Set Screws may cause damage to the inner object which might not be desirable in some applications. (DIN 914)
Flat – Designed for flexibility when frequently resetting or relocating objects on hard steel shafts where minimal damage to the shaft is desired. Affordable and easy to install, Flat point Set Screws can be moved without damaging the inner object. (DIN 913)
Oval – The Oval point is the inverse of the Cup point. The small rounded contact surface allows slight adjustments without loosening the screw and causes minimal surface damage to the inner object. The Oval point Set Screw is the most practical type for situations where the inner and outer objects require regular adjustments.
Half-Dog – Sometimes offered as a Full-Dog point, its protruding tip locks within a mating hole or slot in the shaft, for permanent setting. Half-dog/Dog points are sometimes used instead of a dowel pin. (DIN 915)
Nylon tip – Resembling a Half-Dog point, the soft nylon tip is used to grip curved or textured surfaces.
- What other factors should I consider?
We’ve covered the most common variables including head style, diameter and thread, length, material and plating or finish. Here are a few of the other considerations you might be faced with based on the project and the bill of materials:
Do you need domestic parts (i.e. Holo-Krome) or will imported screws work?
Do you require parts that conform to a specific mil-spec number, such as AN565, NAS1081, MS18063, MS18064, MS18065, MS18066, MS18067, MS18068, MS21342, MS51017, MS51021, MS51022, MS51023, MS51025, MS51026, MS51029, MS51031, MS51033,MS51038, MS51040, MS51045, MS51047, MS51053, MS51476, MS51477, MS51963, MS51964, MS51965, MS51966, MS51973,MS51974, MS51976, MS51977, MS51981, MS51982 with their exacting tolerances and traceability, or will standard commercial parts work?
Does your bill of materials call out a specific manufacturer, such as Holo-Krome or Blue Devil?
Make sure you have the correct installation hardware (Allen wrench or hex key) to go along with your Set Screws.
- What level of certification is required?
Generally, a Certificate of Conformance or a COC is sufficient for your customer. Full certification with material certs, DFARS certification 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 (Holo-Krome) and generic equivalents.
- Custom-made parts per print in non-standard and exotic materials and finishes.
- Inch and metric sizes, including DIN913, DIN914 and DIN915.
For more detailed information about Set Screws, to request a line card, or to send an RFQ, visit our website. And if you don’t see what you need listed, as always, ask us. “Finding the right screw for you” is our tag line after all!
Contact me at firstname.lastname@example.org with your questions, comments or helpful hints!