Threads, Thread Forms, and Points

THREADS Type Notes Machine Screw THREAD FORMING Taptite and Equivalent "Numerous proprietary variants (Taptite II, Powerlok) and generic designs such as DIN 7500. Trilobular thread forming screws can be driven into pilot hole of metal (steel, aluminium) without the expense of a tapped hole. Threads are case hardened to form internal thread in mating part. Good resistance to vibrational loosening properties." Plastite and Equivalent "Numerous proprietary variants and generic designs such as Plastite 45 / 48-2 Plastite trilobular thread rolling screws are used in plastic applications where the thread profile is specifically designed to avoid inducing stresses or boss bursting. Good resistance to vibrational loosening properties." SELF TAPPING Type AB (Fine Thread) "Typically used in thin sheet metal. Often used in white good appliances. Type AB point can start own hole. Type AB are preferred over Type A because they are more effective with brittle materials." Type A (Coarse Thread) Largely replaced by Type AB. Type B For molded or through holes in thin metal, non-ferrous castings. Blunt Point. Hi-Lo (High-Low) "High-Low self tapping screws have a double helix thread. The lower thread for easier penetration into the substrate. The high thread is sharper than a conventional thread. The sharp high thread results in less less displacement of material when it is driven into the substrate. As a result High-Low screws require less effort in assembly. Another benefit of the design is that a large amount of substrate material remaining between the high threads, the smaller minor diameter thread increases contact with the substrate resulting in a stronger grip and increased resistance to pull out and vibrational loosening forces." Type U "Designed to create their own mating threads and permanently fasten metal and plastic parts. Design is preferred in tamper resistant applications." THREAD CUTTING Thread Cutting - Type 25 Designed for use in hard plastics or die castings. The blunt point aids positive location in pilot hole. Slot allows substrate chips to be effectively removed when driving. Thread Cutting - Type 1 â?¦.... Thread Cutting - Type 23 Thread Cutting - Type 17 "Type 17 points are designed to pierce and self drive into sheet metal. Cutting a thread into the mating part as it drives. Slot in thread allows for chips to be effectively be remived when driving." Thread Cutting - Type F Woodscrew "Sharply threads on a tapered shank with a gimlet pint. Threads should extend the full length of the screw to the underside of the head." Coach Screw / Lag Screw Coach screws have thread tapering to a point at the tip. Primarily used on heavy wood or fixing metal to wood. POINT TYPES Chamfer Cut Point "Typical point on a hex bolt or set screw. Chamfer is formed in thread rolling process." Rolled Point Typical on machine screws. Oval Point "Typical on set screws. Oval point provides small contact surface on mating part. Typically slected where the screw may be retightened multiple times." Cup Point "Typical on set screws. Larger contact surface on mating part compared to oval point. Optional : Knurls on tip circumference to increase resistance to loosening (knurled cup point)." Cone Point Typical on set screws where a positive location to a drilled hole / indentation. Dog Point Similar to cone point (above). Dog point provides positive location and can withstand larger load. Drill Point Typical on TEK screws. Point acts as a standard drill. Cutting a hole in mating part and then forms a thread when driving beyond the drill point end. Type 17 "Type 17 points are designed to pierce and self drive into sheet metal. Cutting a thread into the mating part as it drives. Slot in thread allows for removal of excess material." Needle Point Sharp point can pierece thin sheet metal without the need of a pilot hole. Threads are self tapping. Type AB / Gimlet Point Point assists in pulling the screw into a pilot hole and starts tapping into mating part. Type B (Z) Point Used on a mating part with a pilot hole. Lack of a sharp point increases thread engagement. Taptite (Type TT) Tri-lobular thread requires a pilot hole. Type 23 Milled slot allows for excess material Type 25 Milled slot allows for excess material Type U (Hammer Drive) Point allows for positive location.I16