What Are The Two Types Of Sheet Metal Screws
Content Menu
● Introduction to Sheet Metal Screws in Manufacturing
● Thread-Forming Sheet Metal Screws
● Thread-Cutting Sheet Metal Screws
● Key Differences and Selection Guidelines
● Design and Installation Practices
Introduction to Sheet Metal Screws in Manufacturing
Sheet metal screws come up all the time in manufacturing work, especially when joining thin gauge materials in things like duct systems, vehicle body panels, household appliances, or equipment housings. These fasteners make it straightforward to connect parts without always needing separate nuts or pre-tapped holes.
They work well on metals ranging from very thin foils around 0.015 inches thick up to roughly 0.200 inches, and sometimes beyond with proper hole preparation. Unlike standard machine screws that require matching threads already in place or wood screws optimized for fibrous materials, sheet metal screws generate their own threads during installation. That’s what makes them part of the self-tapping family.
The main division falls into two categories based on thread creation: thread-forming and thread-cutting. Thread-forming pushes the material aside to shape threads, while thread-cutting removes small amounts to clear a path. This difference impacts joint reliability, installation effort, material suitability, and long-term performance under loads or vibration.
Thread-forming often uses specialized shapes like trilobular profiles to ease material flow. Thread-cutting incorporates slots or flutes for chip removal. Standards cover these under classifications like ASME B18.6.4, with designations such as AB, B for forming styles and F, 23, 25 for cutting. But the core split remains forming versus cutting.
Thread-Forming Sheet Metal Screws
Thread-forming screws displace the base material rather than remove it. They often feature a rounded or lobed thread cross-section that presses the metal into the thread valleys.
In softer or more ductile sheets, this creates a strong interlock without loose particles. Common in aluminum panels or mild steel casings, where the material flows easily around the screw.
For example, in control box assemblies, engineers use #8 thread-forming screws with pan heads to secure covers to frames. The tight fit from displacement helps maintain electrical grounding and resists loosening from machine vibrations.
Another frequent setup involves galvanized steel in air handling units. Here, thread-forming screws join overlapping sections, and the compression seals edges against air leaks.
In white goods manufacturing, like refrigerator shells, these screws attach internal brackets without damaging enamel coatings, since no chips scratch surfaces.
Trilobular designs, such as those from major suppliers, start easily in pilot holes and build prevailing torque as material fills the lobes.
In vehicle trim work, they hold plastic clips to sheet metal posts, providing reusable connections for service access.
The process requires higher drive torque but yields excellent strip-out resistance. In thin aluminum, pull-out forces often exceed those from cutting types due to full material engagement.
No debris makes them suitable for sealed electronics racks, where particles could cause shorts.
Thread-Cutting Sheet Metal Screws
Thread-cutting screws include flutes or slots that act as cutting edges, removing material to form clean threads.
This suits harder or less ductile metals where displacement might cause cracking or excessive torque.
Type F or Type 23 styles have single or multiple flutes for chip evacuation. As the screw turns, shavings move up the slots and out the hole.
Stainless steel enclosures in processing plants often use these to avoid galling during installation.
In roof assemblies, hex head cutting screws with washers secure panels to supports, handling variable steel hardness.
Cast aluminum parts, common in pump housings, benefit from cutting action that reduces stress concentrations.
Heat shields in exhaust systems attach with cutting screws to thicker brackets, ensuring reliable torque in high-temperature cycles.
Multiple flute designs handle heavier chip loads in thicker gauges.
Lower installation torque compared to forming types allows use with standard tools on assembly lines.
Chips require management in clean applications, but performance in brittle materials outweighs that.
Key Differences and Selection Guidelines
Material ductility guides the choice. Ductile thin sheets favor forming for superior vibration resistance and reusability.
Harder or thicker sheets need cutting to prevent binding or fracture.
Torque requirements differ markedly—forming demands more power, influencing tool specs.
Joint strength tests show forming higher in soft metals, cutting consistent across hardness variations.
Cost considerations include specialized forming geometries versus standard cutting profiles.
Pilot holes must match: smaller for forming to enable displacement, larger for cutting to allow chip flow.
Design and Installation Practices
Accurate pilot sizing prevents failures—too tight causes breakage in forming, too loose reduces hold.
Head options include pan, hex washer, or flat for various finishes.
Drive types like Torx improve engagement over Phillips.
Materials range from zinc-plated steel for general use to hardened stainless for cutting in tough substrates.
Coatings enhance corrosion resistance or lubricity.
Always validate with prototypes, checking torque curves and pull-out values.
Avoid common errors like excessive speed causing heat buildup in forming.
Industry Applications
In automotive, forming dominates interior attachments, cutting handles structural or exterior.
HVAC relies on both for ducts and frames.
Appliances prefer forming to combat operational vibrations.
Electronics favor forming for chip-free assembly.
Construction uses cutting for robust outdoor fixes.
Conclusion
The two core types of sheet metal screws—thread-forming and thread-cutting—each address specific needs in manufacturing.
Thread-forming excels in ductile thin materials, delivering tight, vibration-resistant joints without debris.
Thread-cutting manages harder substrates effectively, providing reliable threads through material removal.
Selecting appropriately considers material properties, thickness, environment, and assembly constraints.
Proper application leads to durable connections, reduced failures, and efficient production.
These fasteners remain fundamental in holding modern assemblies together across sectors.