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 fastening system for a metallic cellular shipping container floor includes a potted insert with a body disposed between a top flange at one end and a bottom flange at another end. The body defines a channel from the top flange leading towards the bottom flange and has a depth not exceeding a distance from the top flange to the bottom flange. The system also includes a hole formed in a panel of a metallic cellular shipping container floor with a depth identical to or greater than a distance from a top portion of the top flange to a bottom portion of the bottom flange. Finally, the system includes a self-tapping screw disposed within the channel of the potted insert, and including a threaded shaft with tip at a distal end of the shaft, and a screw head at a proximal end of the shaft.

In order to prevent wood fringes at the edge of a hole from a countersunk screw (1), the screw-head (2) is provided with a tapering underside and inclined milling-ribs (8) on the tapering underside. Each milling-rib (8) has a planar front-side (15) delimited by smoothly curved convex milling-edge (17) for milling the material during countersinking of the screw-head (2).

A self-drilling screw structure comprises a screw head and a screw rod extending outwardly from the screw head. The screw rod is formed with a drill bit section at one end opposite to the screw head, a drill tail section and a screw thread section. The drill bit section comprises two first cutting edges extending helically and intersecting at a chisel edge. Two first chip flutes located at the positions respectively between the two first cutting edges and extending from the chisel edge toward the drill tail section. The drill tail section comprises two second cutting edges extending helically toward the screw thread section. Two second chip flutes located at the positions respectively between the two second cutting edges and extending helically toward the screw thread section. Each first chip flute and the second chip flute form a connection at joint between the drill bit and drill tail sections.

A wood screw structure comprises a screw head section, a rod section, a first screw thread and a plurality of crushing rib units. The rod section is sequentially integrally formed from the screw head section and comprises a first rod portion connecting the screw head section, a second rod portion, a third rod portion, and a tapered portion extending and tapering outwardly from the third rod portion. The first screw thread is disposed spirally and is protruded on an outer peripheral surface of the tapered portion, the second rod portion and the third rod portion. The crushing rib units are disposed spirally and protruded around the outer peripheral surface of the third rod portion and the tapered portion, and each of the crushing rib units includes a plurality of crushers protrudingly disposed on a rib body. A first discharge gap is formed between the crushers.

A wood screw is disclosed herein. It comprises a screw head and a rod body integrally extended from the screw head and having a shank part and a screwing part, wherein the screwing part comprises a straight surface surrounded with a threaded section and a cutting section on which a cutting unit is formed, and wherein a root diameter of the shank part is larger than root diameters of the threaded section and the cutting section respectively, and larger than or equal to a maximum outer diameter of the cutting section defined by the cutting unit.

A screw, especially for wood, has a knurled region (10) with two sets (11A, 11B) of ribs (11) that are offset from each other by an azimuth angle. For example, the two sets of ribs extend towards each other from opposite ends (10A, 10B) of the knurled region (10) and are intertwined only in an overlap region (12) that is at the middle of the knurled region.

In order to prevent wood fringes at the edge of a hole from a countersunk screw (1), the screw-head (2) is provided with a tapering underside and inclined milling-ribs (8) on the tapering underside. Each milling-rib (8) has a planar front-side (15) delimited by smoothly curved convex milling-edge (17) for milling the material during countersinking of the screw-head (2).

A method for forming a stop flange on a self-tapping screw includes locating a shank of a self-tapping screw between two threading dies, fixing one of the two threading dies and moving the other one of the two threading dies to work the shank, the external thread forming section of each of the threading dies performing threading to form an external thread on the shank, inserting the insert and the recessed corner of each of the threading dies into a top of the external thread to form a groove in the shank, and the insert of each of the threading dies gradually squeezing downward an extruded portion that is formed during formation of the groove to form a stop flange on the shank. Thus, the shank is integrally formed with the stop flange, to stop an excessive movement of the external thread.