What are the differences between cut and rolled threads?

Are the threads cut or rolled? We are often asked this question in regards to how the threads were manufactured on a particular size bolt or screw that we stock. The main reason we are asked this question is because “rolled” threads are perceived to be superior to “cut” threads on externally threaded fasteners.

When a thread is rolled, it means the thread was formed by cold forming the steel by pressing the part between either two flat plates or round dies that have the thread pitch machined onto their face. As the part “rolls” through the dies, the pressure applied by the plates creates the thread without cutting or removing material.

A cut thread (also called a machined thread) is made by machining away the material in order to create the thread form. Cut threads, as the name implies, are made by cutting away material.

Customers who ask this question are typically looking for a product that they can offer their customer that has the highest perceived quality.

The reason rolled threads are perceived to be better than a cut thread is:

     • Thread rolling dies create a thread form that has a rounded root radius.

     • The rolling operation forces the steel’s “grains” to flow with the thread form.

     • The cold working, of the thread rolling operation, increases the strength of the steel in the threads.

When you are dealing with non-heat-treated bolts (grade 2, grade A, low carbon steel, etc.) a rolled threaded part will have a higher strength than a bolt with cut threads in the area where the threads were formed. When a part is heat-treated (like grade 5 and grade 8 bolts) a cut thread and a rolled thread part will have the same strength. The hardness to which the part is heat-treated determines the strength and not how the threads were manufactured.

The form at the bottom (root) of the thread plays an important role in the “fatigue” resistance of the thread. A radiused (rounded) thread root does improve the thread’s fatigue resistance. Cut threads are often perceived to create a sharp point at the thread root.  A sharp point at the root does make a thread more susceptible to fatigue failures as compared to a thread with a round root. Threads can be cut using a cutting tool that has a radiused point to create a rounded root thread. A heat-treated bolt with a cut thread that has a rounded root radius will have a comparable fatigue strength as compared to a heat-treated bolt with a rolled thread.

The fact is that a cut thread can be manufactured with a radius root that is equivalent to the radius root formed by a rolled thread. So for grade 5 and grade 8 strength level products, a cut thread can have the same fatigue resistance as a rolled thread.

Rolling the thread is a cost-effective way to make threads in high-volume operations. A cut thread is the most cost-effective way to make a thread for low-volume applications.

Earnest standard product is made with threads that are rolled prior to heat treatment. When we make a special, we will cut the threads. When we cut threads, we use cutting tools that will create a rounded root thread form that will provide fatigue resistance equivalent to a rolled thread product.

The best thread form (called the aircraft quality thread) is to roll the threads after heat treatment with a large root radius, called a UNJ thread form. A grade 5 or 8 strength level bolt that has had its threads rolled after heat treatment will provide the highest resistance to fatigue failures.  If the parts have been heat-treated after the thread forming operation, the way the threads were manufactured (cut or rolled) does not provide a significant increase in the fatigue resistance.

What is a Place Bolt and how is it used?

Fasteners that create a “locking” action are commonly used in applications that experience high vibration or flexing to ensure that the assembly does not come loose over time. Many of our customers are aware of the choices that are available in locking nuts (All Metal Lock Nuts, Nylon Insert Lock Nuts, etc) but when it comes to the bolt or screw that is used in the assembly, the choices for a locking screw are limited. The two main styles of locking screws that are used in the industry are the Hex Serrated Flange Screw or a Hex Bolt that has a nylon or chemical patch applied to the threads.

Both options have limitations for use in some applications. For example, Hex Serrated Flange Screws can mar the surface that they are being assembled onto, causing premature rusting. Additionally, chemical patches can be adversely affected when exposed to chemicals or heat. Many of our customers are not aware of another option when it comes to a bolt that can create a locking action within your assembly. 

Typically, Place Bolts are used on the inside of engines and transmissions where a loose assembly would result in a major repair. Often, this style of fastener is chosen to assemble the flywheel to the torque converter on most transmission assemblies due to the constant speed changes and excessive vibrations that can be encountered within this application. 

Earnest Machine’s line of Place Bolts are made to the dimensional requirements of the General Motors standard for Type AA Hex Head Lock Bolts. Additionally, Earnest Machine’s line of Place Bolts are also manufactured from high-strength alloy steel and are through-hardened to the Grade 8 strength level as specified in the Society of Automotive Engineers standard SAE J429.

So, whether you are designing a new assembly or trying to improve an existing one, a Place Bolt is an excellent choice for when you want to achieve maximum resistance to vibration, preventing your assembly from loosening over time, and greatly reducing the likelihood of a major failure or repair. 

To learn more about Earnest Machine’s line of Place Bolts, download the spec sheet or speak to an Earnest Sales Representative at +44 (0) 1902 711041. 

Sustainability in the fastener industry.

Scrutinized by the European Union, regulated by the state of California, and labeled a “carcinogen to workers” by the Occupational Safety and Health Administration (OSHA), zinc yellow with hexavalent chromate has become a term industrial fastener buyers must be aware of, as environmental safety and sustainability become front and center policy in most every global organization.

Zinc yellow fasteners with hexavalent chromate are common, as the plating has attractive anticorrosive properties that can be used for a wide variety of applications. While such fasteners are not outright banned for sale, industrial buyers are avoiding them.

According to OSHA, workplace exposure to hexavalent chromate may cause lung cancer in workers who breathe airborne hexavalent chromate. In addition, it may cause irritation or damage to the nose, throat, and lungs if ingested at elevated levels. Direct skin contact with hexavalent chromate can cause non-allergic skin irritation. Contact with non-intact skin can also lead to chrome ulcers, which are lesions on the hands or in the nasal cavity.

Much of the risk is borne by workers who are in and around the processing and plating of fasteners using hexavalent chromate. Which means that such fasteners, if restricted, may be less available, if available at all. Thus, zinc yellow fasteners may not be available if the demand for hexavalent chromate falls; buyers will need to be prepared to source alternatives. The team at Earnest Machine is ready to help you source alternatives to zinc yellow with hexavalent chromate. Call +44 (0) 1902 711041 to speak with an Earnest Machine sales representative for available options.

For more information on what steps have been taken to limit the impact zinc yellow with hexavalent chromate has on the environment and human health, download our whitepaper on “Sustainability in the fastener industry.” 

Back to Basics with Plow Bolts

Is it Plow or Plough Bolts? Whatever you call them, the Plow Bolt definition is a threaded fastener with a low-profile head that includes a feature like a square, keyway, etc, which permits the bolt to be held in position while the nut is tightened. 

Over the years, different manufacturers used varying bolts that had different heads to attach the blades to their machinery. This resulted in a general overuse of the term ‘Plow Bolt’. To differentiate the many Plow Bolt head types, fastener standards organisations assigned numbers to help identify them, ranging from #1 head to #11 head.

Bespoke Plow Bolts are usually needed when special attachments are designed for use on construction equipment. If the original equipment bolt does not fit the application, then specially designed bolts can be provided by Plow Bolt manufacturers like Earnest. 

How are Plow Bolts measured?

When measuring the length of a plow bolt, you include the height of the head in the length measurement (unlike a hex bolt or carriage bolt where you only measure from the bearing surface under the head to the end of the bolt).

What are the most common Plow Bolts used today?

As mentioned above, there are different Plow Bolt head types, ranging from #1 – #11. However, bolt types #1 and #2 were used by companies that are no longer functioning, and so are practically obsolete. The most commonly used bolt heads are #3 and #7. 

The #3 Domed Head Plow Bolt has a heavy-duty head design that provides greater wear resistance and better engagement in square holes. Earnest offers #3 Head Plow Bolts in either a flat head, domed head, or oversized head style.

Earnest Machine stock #3 Head Plow Bolts in Grade 5, Grade 8 and 170M, which is commonly referred to as Grade 9. The 170M product is designed to be stronger and more durable than the Grade 8. It provides excellent resistance to the more abrasive plow applications.

Earnest’s range of Plow Bolts are available in imperial and metric sizing. They are usually measured against the imperial US spec, ASME B18.9, and the metric German spec of DIN 605. Earnest’s range is mainly imperial, but metric is also available, along with bespoke designs.

For more information on Earnest’s Plow Bolt range, or to discuss any bespoke needs, please contact the team to see how we can help.

Lock Nuts: A simple overview

Contrary to what the name implies, Lock Nuts will not be permanently fixed to the mating bolt or screw. Instead, this style of fastener is actually made to resist loosening caused by vibration and will not come apart easily. As an added bonus, this style of fastener is also reusable.

They can be separated out into two basic categories.  All Metal and Nylon, with varying styles of each.

Nylon Lock Nuts

These typically hold an elastic nylon ring that prevents any loosening in vibrating applications. The nylon ring provides a full 360 degrees of locking action, meaning it can grip the bolt or screws threads securely around the entire diameter, unlike All Metal Lock Nuts which only grip from two or three points.

The nylon ring also provides a host of other benefits, such as its dampening effect – which helps absorb and displace vibration, its resilience which adds to its reusability, and the fact that it’s heat resistant of up to around 120 degrees Celsius (250 degrees Fahrenheit).

Earnest provides these types of products within this category:

• Nylon Insert Lock Nut
• Nylon Insert Hex Flange Lock Nut
• Nylon Patched Nut

Typically, Lock Nuts are more expensive than standard Hex Nuts due to the addition of the locking feature. It’s possible to add a chemical patch to a Hex Nut, which will mean it then acts as a Lock Nut. Although this method can save money and stocking space, a chemical patch will only work once, unlike official Lock Nuts, which are reusable.

It’s also important to note that chemical patches also come with an expiration date; they’ll usually need to be used within one to three years.

As an alternative option, you can apply a Loctite-style chemical patch at the time of assembly, like other patches however, this offers no reusability and can only be done once.

Lock Nuts are the perfect fit for any application that involves vibration. You can see them used across a wide range of industries, including automotive, construction, agriculture, aerospace and so much more.

If you want to find out more, or to discuss Earnest’s range, contact the team today. Alternatively, you can view our catalogue here.