A fully threaded screw with a blunt end and usually used with a nut or driven into a pre-tapped hole or threaded insert.
Machine screws are extremely versitile fasteners with standardized threading and that come in a variety of sizes, materials, head styles and drives to best suit the specific application.
Machine Screw Head Styles Include:
- Round Head: Round Head Machine Screws: The head offers a flat bearing area with a rounded top, often used for decorative purposes. This head style has been largely replaced by other styles.
- Pan Head: Pan head machine screws have a flat bearing area and slightly rounded top. It is slightly flatter and has a greater thickness near its circumference than the round head. The additional surface area improves the grip of the driver bit particularly for slotted or flat drivers. Also the larger head increases torque when turning.
- Oval Head: Oval head machine screws, often called oval countersunk, have a tapered base similar to a flat head, but with a sightly rounded head that lies slightly above the surface. These are ideal for countersunk holes, where they have a better profile than round head machine screw heads with a little more of a decorative finish than a flat head. Because they are countersunk, they help the machine screw to center. These heads are often combined with countersunk finishing washers for holding thin materials in place without damage.
- Flat Head: Flat head machine screws have a tapered base and a flat surface that sits flush or slightly below the surface when installed and helps the machine screw to center. This require a pre-drilled counter sink - usually angled at 82 degrees (Unified thread). Metric flat heads have 90 degree angles. For a more decorative finish an oval head might be better suited as it has a slightly rounded top that remains above the surface.
- Fillister Head: Fillister head machine screws is similar to the round head, but have a slightly smaller diameter to allow a deeper slot that suits high torque applications increasing the amount of pressure on the bearing surface.
- Binding Head: Binding head machine screws have a large, flat head with an undercut base. This ideal for electricians in order for them to easily and effectively bind electrical wire.
- Truss Head: Truss head machine screws have a low, a flatter and wider than a typical round or pan head, covering a larger bearing surface area. This offers an alternative to using a washer for holding thin material with large amounts of force. These are commonly found on license plates.
- Hex Washer Head: Hex Washer Head machine screws have a built in washer increasing the bearing surface area which distributes the force overa wider area.
Machine Screw Drive Types:
- Slot drive:Slotted drive machine screws have a simple slot, requiring a standard slotted screwdriver bit. The main disadvantage of slotted drives is that the driver bits easily cam out.
- Phillips drive: Phillips drive machine screws reduce camming to some degree. These drives were actually designed to cause the bit to cam out in order to prevent over-tightening.
- Square drive: Square drive machine screws, also known as Robertson drive, have a square recess in the head of the screw. This drive style reduces the risk of camming out, and allows the use much higher torque for tightening. For additional information about the square drive recess including dimensions and technical specifications, click here.
- 6 lobe/Torx/star drive: These machine screws, which contain a recessed, six-pointed star, requiring a Torx driver bit. They are designed to handle higher torque during installation, making this drive type popular in the automotive industry.
- Hex head: Hex head machine screws offer an advantage where access is limited. Furthermore a wrench or socket wrench can be used to tighten them, and they can be tightened using high torque and thus ideal for high force applications.
Machine screws are available in steel with a variety of different head styles (binding, fillister, flat, hex, hex washer, oval, pan, round and truss) and drives (phillips, slot, 6-lobe, square, hex) and finishes (clear zinc, yellow zinc, black zinc, green zinc, black oxide, nickel plated) and in stainless steel and in nylon. Steel machine screws also available with metric threading. All machine screws feature standard "machine" points, and are available in sizes from #2-56 to 1/2" and lengths from 1/8" to 6".