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Why You Shouldn’t Over-Torque Fasteners

Why You Shouldn’t Over-Torque Fasteners

Everyone who has ever worked with fasteners has accidentally messed one up at some point. One of the most damaging ways to do that is by over-tightening, or over torquing the fastener. This can result in stripping screws, snapping screw heads and damaging pre-tapped threading.

Fastener Torquing

Installing fasteners is an easy task (usually). To do so, you normally apply torque to the fastener, usually a nut or a screw head and simply “screw it in”. When torque and pressure is added to the driver, the fastener begins to spin. In general, although there are exceptions such as the left-hand nut, spinning to the right tightens and spinning to the left loosens (“righty-tighty, lefty-loosey”). The problems start when fasteners are driven too far, or over tightened.

Proper torquing of a flat head deck screw and an over-torqued flat head deck screw

An easy way to picture over-torquing is to take a look at deck screws. Most deck screws have a flat head style. This means when installed correctly, the screw head is supposed to be flush with the surface of the wood. As you can see in the picture to the right, if the fastener is over-tightened, the head is pulled beneath the surface of the wood. The increased surface area pushing against the wood is enough to greatly increase the required torque to tighten or loosen the fastener, which can result in stripping, snapped heads or thread damage which compromises the integrity of the fastener.

When torque is applied to a fastener and it is tightened, it will take an increased amount of torque to further tighten. Most inexperienced people working with fasteners tend to severely over-tighten fasteners thinking it will prevent them from loosening, however, this is not normally the case, and will cause damage to the fastener. To keep a fastener from loosening over time due to vibration and other external factors, a threadlocker solution, locking washer, locking nut or a combination of the three should be used.

While this seems simple enough, when torque is applied to a fastener and it is tightened, it will take an increased amount of torque to further tighten. Most inexperienced people working with fasteners tend to severely over-tighten fasteners thinking it will prevent them from loosening, this is not normally the case. To keep a fastener from loosening over time due to vibration and other external factors, a threadlocker solution, locking washer, locking nut or a combination of the three should be used.

Things to Consider When Torquing Fasteners:

  • Fastener Materials
  • Installation Materials
  • Thread Type

Fastener Materials

When torquing a fastener, the driven portion of the fastener – drive recess or nut – is put under a tremendous amount of stress. This is why it is crucial to use the proper drive size and style on the fastener. Using the wrong size will place an uneven pressure on the recess resulting in a stripped recess or a rounded nut. Since fasteners can be made from different materials ranging from soft metals to heat-treated hardened ones, the torque that can be applied to the fastener will depend on the material the fastener is made out of. For example, an aluminum bolt will not be able to take nearly as much torque as a Grade 8 bolt.

Fastener Drives

The fastener drive style will also matter. Below are the most common fastener drive styles listed from best to worst in terms of torque-taking ability and resistance to stripping:
Drive Styles: Slotted | Phillips | Square | Hex | Star

  1. Star (Torx)
  2. Internal Hex
  3. Robertson (Square)
  4. Pozi-Driv
  5. Phillips
  6. Slotted

Installation Materials

Installation materials can range from plastic all the way to steel which means not only does the torque the fastener can handle matter, the torque the material threading can handle also matters. Torquing a screw in plastic will have a much lower threshold then torquing a screw in steel.

In many installations, ruining the installation hole can end up ruining an entire build. By over-torquing in a softer material, the tapped threading in the hole can be damaged or stripped entirely. This is very common when working with plastic holes. It is generally very easy to over-torque and destroy the threading. To fix this, new threads need to be installed either by re-tapping the whole, or using a threaded insert and more than likely, the diameter of the screw will also need to be increased.

Thread Type

Thread type can also make a difference when it comes to torquing fasteners. There are two basic types of threading:

  • Coarse
  • Fine

Coarse Threading is a deeper but more spread out threading. This makes coarse threaded fasteners more durable because light marring on the threading won’t prevent the threads from spinning.

Fine Threading is a shallower threading but with many more threads per inch. Their tighter and shallower structure makes them less likely to be vibrated loose, but it also means there are more threads holding the fastener in place. Due to these extra threads, the fastener can withstand more torque and distribute it better on the installation material’s threading.

Both types, if torqued too much can cause the threading to slightly warp making it very difficult to remove the fastener later. That warping also weakens and changes the holding power of the fastener.

Torque WrenchThe Best Way to Avoid Over-Torquing

For most DIY projects the best way to avoid over-torquing is just to practice. With practice, knowing when to stop torquing will become second nature.

A torque wrench is a wrench that digitally sets and senses the torque. Once the optimal torque is reached, the clutch inside the wrench will slip preventing the fastener from being tightened further.  Many professional industries follow these torquing guidelines and use these tools to prevent over-tightening.

What Is Pozidriv? How Does It Differ From A Phillips Drive?

What Is Pozidriv?Pozidriv bit and Pozidriv screw

Pozidriv, commonly spelled incorrectly as “Pozidrive”, is an improved variation on the Phillips drive design. After the patent for the Phillips head expired, the company GKN Screws and Fasteners created the Pozidriv design.

The Pozidriv drive style was originally formed to address the largest issue Phillips heads are prone to: cam-out. Cam-out is defined as the slipping out of a drive recess that occurs when torque exceeds a certain limit. The Pozidriv drive style has the same self-centering design of a Phillips drive style but improves upon the two following factors:

  • Increased torque without cam-out
  • Greater surface contact engagement between the drive and the recess in the fastener head making it harder to slip when installed correctly

Can I Use a Pozidriv on a Phillips Screw? Or Vice-Versa?

While we at Albany County Fasteners do NOT recommend using the improper drive style on a screw, technically speaking you can. A Phillips drive style fits into a Pozidriv drive recess decently when using the right size. It’s important to note that even if the Phillips does fit snugly into the drive recess, it is still much more likely to strip or cam-out than when using the proper driver.

Alternatively, you can attempt to remove a Phillips screw with a Pozidriv drive but they do not fit into the Phillips drive recess snugly and are much more likely to slip or damage the recess during removal.

Where Are Pozidriv Screws Used?

Pozidriv screws can be used just about anywhere, although they are not nearly as popular as standard Phillips screws. Over the years, many other drive styles, such as the Torx and Robertson, have come out as being more reliable than the Phillips drive style at preventing cam-out and stripping. The Phillips drive is still extremely popular in manufacturing due to its self-centering design but is starting to lose popularity for manual applications due to other drive styles having a better design.

Benefits of the Pozidriv Drive Style

As an improvement on the Phillips drive style, the main benefit of using the Pozidrive is the increased torque without the increased risk of cam-out. Pozidriv screws can handle significantly more torque on the fastener recess than a Phillips drive can.

How Do You Identify A Pozidriv Screw?

While Phillips and Pozidriv screws look similar, Pozidriv are actually quite easy to recognize at a glance. This is due to four notches marked into the head of the Pozidriv screw that are not present in the Phillips Head Screw.

Phillips Pozidriv
Phillips Drive Recess Profile Pozidriv Drive Recess Profile



Pozidriv Screwdrivers

The Pozidriv drive style can be found in a range of sizes from 0-5. The letters PZ or PSD are usually listed before the size number (e.g. PZ3 or PSD5). ANSI standards refer to Pozidriv as a “Type IA”. The Pozidriv style can be found in two forms. Either as a Pozidriv screwdriver or as a Pozidriv screwdriver bit. We currently carry Pozidriv driver bits in several different sizes in the following Vega Bit Kits:

Pozidriv vs.

Phillips

The Pozidriv is an improvement on the Phillips drive by increasing its torque capacity without increasing the likelihood of cam-out. It also has greater surface area contact with the drive recess. This makes it less likely to strip when installed correctly. In general, you can determine if a Pozidriv screw should be used over a Phillips screw by asking the question “How much torque do I need for this installation?” If the answer is a minimal amount of torque, the Phillips drive will work, otherwise, use the Pozidriv. As an improvement on the original Phillips style, the Pozidriv style is better than the Phillips.

Torx

The Torx, or Star, drive style vastly changes the design of the drive recess. Due to the star having six points of contact (6-Lobe), the screw uses a truly radial force rather than an axial force. Phillips and Pozidriv screws use an axial force to drive the screw which is not as effective and is more likely to cause cam-out. For manual applications, Torx screws are quickly becoming the most popular choice.

ROBERTSON

The Robertson, or square, drive is quite common especially throughout Europe. The square drive offers a unique style as it must fit perfectly into the drive recess to drive properly. When it comes to Robertson vs. Pozidriv styles for manual applications, the Robertson is the winner. However, the square drive is not nearly as popular as the star drive style.

Conclusionpozidriv screw and pozidriv insert bit from Vega set

While the Pozidriv drive style is an improvement upon the Phillips drive style, the Phillips is still incredibly popular and does not seem to be going anywhere any time soon.

Should you be in the manufacturing field and find you are having trouble with cam-out, you may want to attempt a Pozidriv configuration. It will give you the added benefits of a reduced cam-out with a better fit into the drive recess while preserving the self-centering functionality that is a must for manufacturing. For manual applications however, both the Star and Square drives are better choices to better suit your needs.



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