Thread Cutting & Floorboard Screws
What Are Thread-Cutting Screws?
Thread-cutting screws are self-tapping fasteners that create mating threads in a pre-drilled hole as they are driven. They’re used when you want the speed of a tapping screw but need a machine-screw style thread in metal, plastics, or composites.
Thread-Cutting vs. Thread-Forming vs. Self-Drilling
- Thread-cutting: removes material (produces chips) to cut threads in the pilot hole; best for metals and harder plastics.
- Thread-forming: displaces material (no chips) to form threads in softer materials like many plastics or thin sheet.
- Self-drilling: includes a drill point and can make its own pilot hole in thin sheet metal; not the same as thread-cutting.
Types of Thread-Cutting Screws
- Slotted Hex Washer Head Thread-Cutting Screws: dual-drive (slot + hex) heads with an integrated washer for fast assembly and wide bearing area—popular in sheet-metal work and service installations.
- Floorboard Screws: a heavy-duty thread-cutting style used in automotive and industrial flooring/panel applications. The large hex-washer head spreads load and allows driving with a wrench or screwdriver.
- Other point styles (by application): common thread-cutting families include Type F (for heavier gauges and castings), Type 23 (thin sheet), and Type 25 (plastics and soft metals). Select by base material and pilot-hole guidance.
Materials & Finishes
- Black Phosphate Steel: low-glare finish used indoors; typically paired with oil for additional protection.
- Zinc-Plated Steel: bright finish for dry interior environments and light corrosion resistance.
- Stainless Options (availability varies): certain thread-cutting patterns are offered in stainless for improved corrosion resistance.
Sizes, Threads & How to Specify
Order by diameter × thread × length (e.g., #10-24 × 1-1/2″, 1/4″-20 × 1″, or M5-0.8 × 25 mm). Length is measured from under the head to the tip—flat (countersunk) heads are measured overall. Choose the head/drive style to match your tools and required bearing area.
Common Applications
- Sheet-metal fabrication, ducting, enclosures, and brackets
- Automotive panels and floorboard assemblies
- Electrical, HVAC, and appliance mounting
- Plastic housings (use the point style suited to the resin)
Installation Tips
- Always drill a pilot hole to the size recommended for the screw type and base material.
- Deburr and clear chips from the hole; cutting screws create chips that should not remain in the joint.
- Drive perpendicular to the surface; avoid over-torque that can strip the new threads.
- Use lubrication when cutting into steel or tough alloys if permitted by the application.
- For plastics, use the point style intended for your resin and drive at controlled speed to limit heat.
Related Hardware
- Finish, flat, and fender washers for added bearing on thin materials
- Thread-locking methods (prevailing-torque nuts, chemical threadlocker) where vibration is present
Thread-Cutting & Floorboard Screws FAQs
See the accordion below for pilot sizes, material choices, and when to choose floorboard screws over other head styles.
Disclaimer: This page provides general guidance. Always follow the product datasheet and applicable standards.
A self-tapping screw that cuts machine-style threads into a pre-drilled hole as it is driven.
Thread-cutting removes material and makes chips; thread-forming displaces material with no chips; self-drilling has a drill point to make its own pilot in thin sheet.
Yes. Use the pilot size recommended for the screw type and base material to avoid stripping or excessive drive torque.
Use heavier-duty styles (often called Type F) for thicker steel or castings; Type 23/25 patterns are common for thin sheet and plastics. Match the point design to the base material.
When you need a large hex-washer head for wide bearing and a dual-drive option (wrench or screwdriver), commonly in automotive/industrial floor or panel work.
Hex-washer heads offer strong driving and large bearing; pan or button heads provide a low profile; flat heads sit flush in a countersink.
Black phosphate is typically for indoor use and low glare; zinc plating provides a bright finish and light corrosion resistance for dry interiors.
Certain patterns are offered in stainless for better corrosion resistance. Availability depends on size and head style.
Yes, use the pattern intended for your resin and drive at controlled speed to reduce heat and cracking; in many plastics a thread-forming style may be preferred.
Reuse is not ideal because the cutting edges can dull and the formed internal threads may wear. Replace if performance is critical.
Common causes are an oversize pilot, misalignment, work-hardened material from previous attempts, or dull tools. Verify pilot size and try a fresh screw/bit.
Often the integrated hex-washer head provides adequate bearing; add a washer only when specified or when you need extra surface protection.