Type A Screws: Point Styles, Thread Pitch & Sheet Metal vs Type AB & B Guide
Type A screws (standardized under ASME B18.6.3 and SAE J933) are thread-forming tapping screws engineered with coarse spaced threads and a sharp, conical gimlet point. Specifically designed for joining light-gauge sheet metal (18 to 28-gauge / 0.018" to 0.048" thick), resin-impregnated plywood, plastics, and drywall to wood studs, the sharp gimlet point penetrates and aligns pre-punched or drilled pilot holes effortlessly without requiring pre-tapped mating machine threads.
Type A vs. Type AB vs. Type B Tapping Screws: The Differences
Thread-forming sheet metal screws are categorized into three primary point and thread pitch styles based on metal thickness and material ductility.
Comparing thread geometry, point styles, and material thickness applications:
| Tapping Screw Specification | Point Style Geometry | Thread Pitch & Spacing | Recommended Material Thickness Application |
|---|---|---|---|
| Type A Screw (CLASSIC GIMLET) | Sharp Conical Gimlet Point | Coarse Spaced Threads (Widest Pitch) | Thin sheet metal (18 to 28 gauge), light HVAC ductwork, plastics, soft wood |
| Type AB Screw (MODERN HYBRID) | Sharp Conical Gimlet Point | Fine Pitch Spaced Threads (Same as Type B) | Medium sheet metal (12 to 24 gauge), brittle plastics, structural sheet attachments |
| Type B Screw (BLUNT POINT) | Blunt Tapered Flat Point | Fine Pitch Spaced Threads | Heavier sheet metal (0.050" to 0.200" thick), non-ferrous castings, through-holes |
| Type F Screw (Thread-Cutting) | Blunt with 5 cutting flutes | Standard Machine Screw Pitch | Heavy structural steel, cast iron, aluminum die-castings |
Type A Screw Dimensional & Thread Pitch Matrix (ASME B18.6.3)
Standard engineering dimensions for common commercial Type A screw sizes:
| Screw Size Gauge | Major Outer Diameter | Threads Per Inch (TPI - Coarse) | Recommended Pilot Hole Drill Size |
|---|---|---|---|
| #4 Type A | 0.114 inches (2.90 mm) | 24 TPI | #44 Drill (0.086") |
| #6 Type A | 0.141 inches (3.58 mm) | 18 TPI | #36 Drill (0.106") |
| #8 Type A (HVAC DUCTWORK STANDARD) | 0.168 inches (4.27 mm) | 15 TPI | #29 Drill (0.136") |
| #10 Type A (COMMERCIAL SHEET METAL) | 0.194 inches (4.93 mm) | 12 TPI | #21 Drill (0.159") |
| #12 Type A | 0.221 inches (5.61 mm) | 11 TPI | #14 Drill (0.182") |
| #14 (1/4") Type A | 0.254 inches (6.45 mm) | 10 TPI | #1 Drill (0.228") |
Head Styles & Drive Recesses Available for Type A Screws
Type A tapping screws are manufactured in diverse head geometries: Hex Washer Head (slotted/unslotted, driving with 1/4" or 5/16" magnetic nutsetters in sheet metal HVAC), Pan Head (Phillips/Torx star drive for general assembly), Flat Countersunk Head 82° (for flush mounting in door hinges and hardware), and Oval Head (for automotive trim).
How to Size and Drive Type A Sheet Metal Screws in 4 Steps
Pilot hole drilling and torque fastening.
Step 1: Determine Sheet Metal Gauge Thickness (18 to 28 Gauge)
Verify metal is under 0.050" thick to prevent screw stripping or binding.
Step 2: Drill the Correctly Sized Pilot Hole Using an HSS Drill Bit
For a #8 Type A screw, drill a #29 (0.136-inch) pilot hole through both sheets.
Step 3: Chuck a Magnetic 1/4" or 5/16" Nutsetter onto a Clutch-Driven Drill
Set drill clutch to medium torque to avoid stripping the formed sheet metal threads.
Step 4: Drive Screw Plumb at Medium RPM Until Hex Washer Flange Clamps Tight
Stop instantly when the washer seats firmly against the metal surface.
Frequently Asked Questions (8 Questions Answered)
Q1: What is a Type A screw?
A Type A screw is a thread-forming sheet metal tapping screw featuring coarse spaced threads and a sharp conical gimlet point, designed for fastening thin 18-28 gauge metals and plastics.
Q2: What is the difference between Type A and Type AB screws?
Type A has coarse spaced threads; Type AB has the same sharp gimlet point but features finer pitch threads, allowing it to grip both thin sheet metal and thicker 12-24 gauge metals.
Q3: What is a gimlet point on a screw?
A gimlet point is a sharp, threaded cone tip that pierces and draws the screw into pilot holes without requiring a separate pre-threaded nut.
Q4: Can you use Type A screws in wood?
Yes, because of their sharp gimlet point and coarse wide-pitch threads, Type A screws hold exceptionally well in softwoods, plywood, and fiberglass.
Q5: What size pilot hole is needed for a #10 Type A screw?
A #10 Type A screw (0.194" outer diameter) requires a #21 drill bit (0.159-inch diameter) pilot hole in standard sheet metal.
Q6: Are Type A screws self-drilling?
No; Type A screws are 'thread-forming' (they form their own threads in pre-drilled or punched holes), whereas self-drilling 'TEK' screws have a drill-bit tip that drills the hole itself.
Q7: What materials are Type A screws made of?
They are commonly manufactured from case-hardened carbon steel with zinc plating, 410 stainless steel (hardenable for sheet metal), or 304/316 marine stainless steel.
Q8: Why are hex washer head Type A screws so popular in HVAC?
The integrated wide washer flange spreads clamping force across thin galvanized sheet metal ducts without puncturing, and the hex head prevents bit cam-out.
Final Thoughts & Key Takeaways
In conclusion, understanding type a screws: point styles, thread pitch & sheet metal vs type ab & b guide provides essential clarity, practical strategies, and actionable advice. By incorporating these foundational insights, adhering to verified safety guidelines, and following structured best practices, you ensure reliable, long-term outcomes while preventing common mistakes. Stay informed, consult certified professionals when needed, and maintain consistent quality care.