Choosing the best fastener material for a particular application requires analysis of several factors. Among these are the conditions under which the nuts, bolts, and screws will operate, their chemical and mechanical properties, their cost, and even their appearance. While no single material is right for every job, the characteristics of steel, stainless steel, brass, and nylon often make each the “right” choice for specific operations. This guide from Mr. Metric can help you choose the threaded fastener that will work best for your operation.
We probably take fasteners—nuts and bolts—for granted until we reach into our toolbox for the right socket wrench for the engine bolt we want to remove. Do we need an SAE socket or a metric one? If we pick the wrong one, it may not work as expected. In fact, if we pick the wrong one, it may just slip around the nut or the bolt head without getting any traction at all. We also run the chance of using say an SAE bolt as a replacement with a metric-threaded nut or hole—or vice-versa.
Why is there a difference? Why have both SAE and metric nuts and bolts been used on American cars over the years? And what’s the situation now and in the future?
A fastener’s strength is determined by two primary factors: 1) the material it is made from, especially the percentage of hardening carbon in the steel, and 2) the process used to create it – usually heat treatments such as tempering, galvanizing, annealing, and quenching. Treating steel fasteners to harden them necessarily reduces their ductility. Bolts, nuts, and screws can be made to fulfill tasks that require specific strengths and ductility, and identifying these properties aids contractors and manufacturers in selectig the right fastener for the job.
Metric fasteners adhere to strength ratings, or Property Classes, mandated by the International Standards Organization (ISO). Imperial, or SAE fasteners’ ratings, or Grades, are assigned by the American Society for Testing Materials (ASTM). Grades and classes are denoted by markings on the heads of externally threaded hardware and the sides or faces of internally threaded parts: Continue reading
Nylon screws, bolts, and nuts are gaining popularity. Available in all metric sizes, they are often found in appliances, electronics, and even industrial-strength uses such as production equipment and automobiles. Threaded nylon metric fasteners can connect and clamp a variety of materials commonly used in construction and manufacturing processes, such as wood, metal, plastic, etc. But, just because they can be used for a particular application does not mean they should be used.
So how do you decide whether nylon bolts and screws offer a viable alternative to more traditional metallic fasteners? The key is to understand nylon’s unique characteristics and the impact they will have on the job conditions and application.
A Mr. Metric customer, Cody Schmidt used a variety of metric fasteners to modify and upkeep his Lulzbot Taz5 3D printer. When he found a modification plan online that he wanted to implement he realized the adjustments needed for the job required very specific bolt sizes that most providers did not offer as they are hard to find or extremely rare.
Cody was very pleased when he learned that Mr. Metric carries a large range of specialty sized bolts, including the exact ones he was looking for. Cody stated:
“The most awkward size bolt I have ever used was used here too. A lonely m3x60mm bolt. But what I learned most importantly was that when reordering some parts, the shipping speeds here help big time.” Continue reading
When looking for ways to reduce waste, cost-conscious and environmentally aware manufacturers and consumers may consider reusing metric bolts and screws. But not all bolts and screws can be safely and effectively reinstalled after being removed from an assembly or component. In fact, an unequivocal “yes” is never the answer to the question of whether a fastener can be reused. Depending on the situation, the answer is always either “no” or “it depends.”
High-strength bolts that have been pre-tensioned into their proof load range – the point at which they permanently deform and do not “snap back” when relieved from their loads – should not be reused. This is the case in many applications, as structural and other bolts used in the manufacturing, construction, and automotive industries are commonly tightened to a torque value that creates a sufficient clamp force to prevent joint failure.
Tamper-proof screws are designed to prevent the dismantling of the products they hold together for safety and/or security reasons. Design developments have made it both difficult to unscrew some fasteners, and easier to determine if a screw has been interfered with. These “tamper-resistant” and “tamper-evident” options have an important place in making products such as electronics, safety devices, security systems, etc., safer, more secure, and less susceptible to vandalism and unauthorized “adjustments.”
The Tamper Resistant Design
Tamper-resistant screws are labeled as such, because their unconventional drive slots require specialized tools to engage and turn them. Holes, notches, and odd geometric shapes are commonly used as drive slots, and can only be driven with their corresponding tools. The theory is that thieves and vandals may keep slotted and Phillips screwdrivers among their burglary tools as a matter of course, but they are unlikely to have access to spanner or Torx drivers when the opportunity for malfeasance arises.
As the revolution in desktop 3D printing for professional and educational sectors continues to grow, the demand for these printers is spreading to the consumer for home use. Individuals operating with a tight budget tend to select 3D printer kits as an entry-level option. The kits require you to assemble the printer and purchase the necessary hardware.
When researching homemade digital 3D printer kits online, you will find all sorts of information posted on blog and forum sites, as well as “how-to” videos on YouTube. In the Thingiverse community, you can learn how to construct your own D-Bot CoreXY 3D printer. The site provides step-by-step instructions, along with the list of components and hardware needed to assemble the printer. Continue reading
Like most aspects of construction and manufacturing, choosing the proper tool for the job goes a long way toward determining the project’s success. Selecting a metric fastener’s drive recess (the slot or hole into which the driving tool is inserted) is no different. Drive recesses, from Phillips head screws to more unusual shapes and specialized uses all have advantages and disadvantages. Take a look at some of the drive types Mr. Metric offers to learn about which style is right for your job.
Ensure Proper Tightening & Removal of Metric Fasteners With the Right Drive Type
Slotted – The first and still one of the most common varieties, slotted metric screws are inexpensive and come in virtually any head shape desired. They are also the easiest to torque when using a screwdriver to remove corroded or frozen fasteners, so they are often used when field installation and/or removal is necessary. However, they are unsuited for automated driving because the single slot allows the bit too much tolerance, and slippage and off-center engagement can occur. Continue reading
Tightening a nut onto a bolt causes the bolt to stretch slightly. Much like a spring, the bolt resists this stretching, and its tendency to return to its natural state creates clamping action between, say a cylinder head and a manifold, or two pieces of sheet-metal housing.
It is critical to the component’s operation that the amount of tension created holds the parts together strongly enough to prevent their separation by outside forces such as the machine’s vibration, the load stress generated during operation, gasket creep, temperature fluctuations, and more. Too much torque, however, can stretch the fastener too much, to the point where it chips, breaks, or yields. Bolts and screws are rated by their “proof load” – how much tension they can withstand before they fail. As a rule of thumb, torque a “clamp load” (also known as “preload”) 75 percent to 90 percent of the proof load is optimal.
CLICK TO MAKE LARGER