A fastener includes a shank defining a shank root, a head, a drilling portion and main threads. The main threads divide the shank root into recessed root sections. Each main thread with two cutting faces which converge at an edge is inclined to a shank axis by 60 to 82 degrees. At least one main lobe projects from the recessed root section and flares outward to at least a midpoint of at least one cutting face between the recessed root section and the edge of the main thread. The inclination allows the main threads to have a large rotating angle for increasing cutting and drilling efficiency. The extension of the main lobe supports the main thread to bear the drilling stress to prevent the shank and main threads from snapping and allow debris accommodation to provide a firm fastening effect.

A drywall screw for fastening a plasterboard panel to a metal support is provided, the screw having a head, a tip portion and an elongate shank, wherein the tip portion adjoins the shank, wherein the drywall screw has a widening element for widening the first borehole in the plasterboard panel to a first borehole diameter t and breaking off upon impinging the metal support, wherein the head exceeds the first borehole diameter t with a pressing-in volume V.sub.1, wherein the shank has a thread-free underhead portion which falls below the first borehole diameter t with a receiving volume V.sub.2 which is at least 80% of the pressing-in volume V.sub.1.

A screw including a shank, wherein a thread helix receiving groove that winds around the shank is provided in the shank, and wherein the shank has a screw tip, and further including a thread helix having a base and a crest, wherein the thread helix and the shank are separate parts, wherein the base of the thread helix is arranged in the thread helix receiving groove, and wherein the crest of the thread helix projects radially from the shank. The crest of the thread helix of the unconstricted screw is displaceable towards the shank by linearly driving the shank, together with the thread helix, into an undersized borehole in a concrete or masonry substrate. A method for installing such a screw is also provided.

A screw includes a head and a shank extending from the head, and a hole-enlarging portion formed on the shank. The hole-enlarging portion features no thread and a substantially triangular transverse section. The hole-enlarging portion includes three inclined edges spaced from one another in the circumferential direction of the shank, and a guiding slope is formed between two adjacent inclined edges. The shank defines a longitudinal axis and is provided with a thread. Each inclined edge extends toward the head in an inclined direction relative to a horizontal axis perpendicular to the longitudinal axis. The inclined direction of each inclined edge is identical to a direction in which the thread extends toward the head.

A screw and anchor assembly include a male fastener and a female anchor. The male fastener only has threads or half-circular fins on half of the surface area. The other half is just like a regular cylinder. The female anchor only has threads or half-circular fins on half of the inner surface area. The other half is just like the inner wall of a regular cylinder. The user may push the male fastener into the female anchor, so the half-circular fins on the male fastener engages with the half-circular fins inside the female anchor and locks the male fastener to the female anchor. When the user needs to remove the male fastener, simply turns the male fastener 180 degrees and disengages the half-circular fins on the male fastener from the half-circular fins on the female anchor, then pull the male fastener from the female anchor.

A screw and anchor assembly include a male fastener and a female anchor. The male fastener only has threads or half-circular fins on half of the surface area. The other half is just like a regular cylinder. The female anchor only has threads or half-circular fins on half of the inner surface area. The other half is just like the inner wall of a regular cylinder. The user may push the male fastener into the female anchor, so the half-circular fins on the male fastener engages with the half-circular fins inside the female anchor and locks the male fastener to the female anchor. When the user needs to remove the male fastener, simply turns the male fastener 180 degrees and disengages the half-circular fins on the male fastener from the half-circular fins on the female anchor, then pull the male fastener from the female anchor.

A fastening nut device for fastening one substrate to another includes a cylinder, which is circumferentially larger proximate to a first end thereof, thus defining a first section and a second section of the cylinder. External threading, which is reversed, is positioned on the second section and extends from a second end of the cylinder. The cylinder can be inserted into a first hole positioned in a first substrate by counterclockwise rotation. The first section of the cylinder abuts a first face of the first substrate and the second end of the cylinder is accessible from a second face of the first substrate. A channel, which is internally threaded, extends into the cylinder from the second end. A threaded fastener, which is engaged to a second substrate, can be inserted by clockwise rotation into the channel to engage the second substrate to the second face of the first substrate.

A sheet metal screw includes one or more of a tapered self-drilling tip, an asymmetric thread angle and/or a trilobular thread edge profile.

A quick fastening screw includes a head, a shank with spirally-disposed thread convolutions, and a drilling portion. Each thread convolution has at least three flank sections and at least three arc sections each formed between any two adjacent flank sections. Two ends of each arc section and the flank sections adjacent to the arc section are respectively intersected to thereby form two joints. Between the two joints is formed a curved cutting portion which forms a radian not more than a quarter of a maximum thread radius so that each curved cutting portion becomes sharp to cut quickly, speed up a screwing operation, decrease the friction between the thread convolutions and a workpiece, and reduce the resistance and torque. The non-circular thread convolutions also receive cut debris efficiently and prevent the cracking of the workpiece caused by the undue accumulation of the debris.

A quick fastening screw includes a head, a shank with spirally-disposed thread convolutions, and a drilling portion. Each thread convolution has at least three flank sections and at least three arc sections each formed between any two adjacent flank sections. Two ends of each arc section and the flank sections adjacent to the arc section are respectively intersected to thereby form two joints. Between the two joints is formed a curved cutting portion which forms a radian not more than a quarter of a maximum thread radius so that each curved cutting portion becomes sharp to cut quickly, speed up a screwing operation, decrease the friction between the thread convolutions and a workpiece, and reduce the resistance and torque. The non-circular thread convolutions also receive cut debris efficiently and prevent the cracking of the workpiece caused by the undue accumulation of the debris.