October 30, 2014
What the Heck are Set Screws?
We begin the fourth quarter of 2014 with an introduction to the Set Screw. A Set Screw is a headless screw (appropriate for our Halloween edition) fully threaded from end to end. Traditionally classified within the Socket family of products, Set Screws are comprised of 3 main parts: the drive, the thread and the point. They (generally) have a hexagonal drive on one end, and a point on the other. They are often used in conjunction with a shaft collar, and like their functional relatives, the Dowel Pin, Retaining Ring and Shoulder Screw, they are used as part of an assembly (you should be getting used to reading about assemblies by now :)).
Who uses Set Screws?
Set screws are used in many industrial and mechanical devices, particularly within 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?
The set screw works by exerting compressional force through the tip to prevent the relative movement between the two objects so each part can function as intended. This is different than traditional screws that hold objects together with threads. Who would have thunk that a headless screw could have so much power!
Check out this video for a demonstration of installation and application: https://www.youtube.com/watch?v=U7hragiTmZI
What options are available?
Like most fastening products, the bevy of options is plentiful (and sometimes exhausting if you ask me!). Once the basics like the diameter, thread, length and material are determined, the main decisions that need to be made are the drive and point style.
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. There are 7 (yes 7!) main points that are available, and each serves 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 in place permanently. 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 shaft is necessary. Affordable and easy to install, Flat point set screws can be moved without damaging the inner object. (DIN 913)
- Oval-its 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 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.
Are there other factors to consider?
From what you’ve just read, it appears that the choices are abundant, yet, in practice, many of the combinations that engineers are seeking are only available as specials and have to be custom made. For example, if you are looking for a fine thread cone point set screw in stainless steel, you may be told it has to be custom made with a minimum run and a long lead time. Make sure to check with our sourcing experts first before you change your requirements!
So, you might be wondering how to get what you need and get it fast? 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. The most common material is hardened alloy steel with a thermal black oxide finish, as per ASME B18.3. Socket set screws come standard with 3A thread fit and a Rockwell hardness of C45-53.
Commercial, Mil-Spec or Brand name?
Finally, Set Screws can also show up under their most popular domestic brand name (Holo-krome) or their Mil-spec numbers, which are DFARS compliant with full paperwork. 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.
Set Screws Available at MF Supply:
Here at MF Supply, we offer:
- 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.
For more detailed information on Set Screws, visit us at http://www.mfsupply.com/category_s/1914.htm.
And if you don’t see it listed, as always, ask us. Finding the right screw for you is our tag line after all!