Screws
It could possibly be said when it comes to fasteners, the category of “screws” might be the broadest one there is. There are so many types. Performing all kinds of functions in every industry that there is. We won’t try to cover all of them here but we’ll give a good cross section of what’s out there. Let’s start with machine screws.
Machine Screws
Uniformly threaded screws of ¼ inch nominal diameter or less that are designed to be threaded into uniformly threaded nuts or threaded holes in the parts they are intended to fasten. Machine screws are available in a wide array of configurations, materials, driver head types and sizes. As their name implies, machine screws are used to fasten various components together in machines, tools, appliances, electronic devices and vehicles of every description. They are available in virtually every material including steel, stainless steel, brass and even nylon. Uniform threads maintain the exact same diameter throughout the entire length of the threaded section of the fastener.
This is as opposed to tapered threads with a pointed end such as on wood screws, which are intended to cut their own thread into the softer wooden or plastic material they are being threaded into. Machine screws are available in a wide assortment of driver head types, including standard slotted, Phillips head, hex socket head for use with Allen wrenches, Torx six-pointed star, square-drive socket head and security heads, which are easily driven in but very difficult to remove.
Machine screws are versatile in the number of types of joints they can fasten. They can be used for fastening two or more components with through holes and a nut behind all the components. They can be passed through two or more components and then finally threaded into the rearmost component, which is solid and uniformly threaded and acts as the nut in the joint. Two opposing machine screws can also be used with threaded couplings to separate two plates or boards by the distance equal to the length of the coupling. Machine screws are also used for many types of electrical connections and terminal strips. They are also used to fasten many gasketed devices that are sandwiched together such as waterproof motor casings. They can also be threaded into PEM brand fasteners, which are threaded metallic inserts cast right into plastic parts.
Self Tapping Screws
Self-tapping screws are different to traditional screws as they tap their own threads when screwed into either plastic, wood or metal.Self-tapping screws are commonly used when you need to attach two pieces of material together where you can only access one side of the material. Where you can access both sides you can use either a screw or a bolt.Self-tapping screws are useful where you have to disassemble and reassemble products such as furniture, as self-tapping screws will relocate themselves into the same threads which they have been removed from.Blunt nose and flat ended Self-tapping screws require a pilot hole slightly smaller than the screw diameter to be created before they can be driven into the material with a screwdriver. Pointed nose self-tapping screws do not require a pilot hole. The action of driving the screw in will result in the self-tapping screw cutting a thread into the material and securing the materials together. Self-tapping screws are typically used to secure wood, plastic, metal and brick together.Common head styles in self tapping screws are pan, flat, and hex washer head.
Self Drilling Screws
Self-drilling screws are sometimes known by the brand name, Tek® Screws. These screws can be identified by the drill bit shaped point of the screw and are designed for a variety of applications such as fastening metal to metal and metal to wood. Self-drilling screws do not require a pilot hole, which accelerates installation time and lowers the cost and need of additional drill bits. This extra functionality and cost saving feature makes self-drilling screws the clear choice for metal building construction. The drill points are numbers #1 through #5 and the amount of steel they can drill through increases as the numbered point increases. Typically, self-drilling screws are used in light gauge applications but a #5 drill point can drill through and fasten up 1/2″ of steel. During installation, self-drilling screws will also tap threads to a degree.
Thread cutting screws
Thread cutting screws are a type of self-tapping screw that creates new threads in existing holes in metal. Thread cutting screws are commonly used as fasteners in items that need periodic maintenance. Thread cutting screws are most often used with wood and plastic, and do not generate as much stress on the material as thread forming screws.Type 1 point: A Type 1 point thread cutting screw with single flute for general use. Produces a fine standard machine screw thread for field replacement.Type 23 point: A Type 23 point thread cutting screw in the fine thread series offering maximum thread cutting area and excellent chip clearing, with minimum tightening torques.Type F point: A Type F point thread cutting screw with machine screw thread with blunt tapered point, having multi-cutting edges and chip cavities.For heavy gauge sheet metal, aluminum, zinc and lead die castings,cast iron, brass and plastic.Type 25 point: A Type 25 point thread cutting screw similar to type 23 point except with coarse Type B thread. For plastics and other soft materials with large chip clearing and cutting edges.
Thread Rolling Screws
Thread rolling screws are designed for reliable and secure fastening into materials such as plastic. They have a trilobular lobed cross-section, and form threads in pre-existing holes by pushing material outward during installation. When installed in sheet metal, thread rolling screws often require an extruded hole; the extrusion forms a lead-in and provides extra length for improved retention. Thread rolling screws are popular for applications where the loose chips formed by thread cutting processes must be avoided. Thread rolling screws come in a variety of head styles and materials depending on the specific application.