Robertson vs. Slotted
Comparing 2 standards across 9 specifications. 9 key differences identified.
The Robertson drive (Square socket / SCRULOX, standardized under ANSI Type III / CSA B35.4) is a 4-sided tapered square recess drive invented in Canada by P.L. Robertson, patented in 1906-07, with a 1908 manufacturing refinement (cold-forming the socket) that made it commercially viable. Known for its distinct tapered geometry that locks the screw onto the driver bit for one-handed operation, it is the dominant construction and electrical fastener across Canada.
The Slotted drive (Flat Head / Flat Blade) is the original single-slot fastener drive geometry standardized under ISO 2380 and DIN 963. Operated with a flat screwdriver blade, it features no inherent centering or cam-out retention, making it susceptible to tool slippage and strictly limited to manual assembly and decorative restoration.
Specification Comparison Table
9 Parameters| Parameter / Spec | ||
|---|---|---|
|
Standard Specifications
|
CSA B35.4 / ANSI Type III Square Recess / ASME B18.6.3 | ISO 2380 (Screwdrivers) / DIN 963 / ASME B18.6.3 |
|
Drive Geometry
|
4-sided square recess with a slight interior conical taper (approx. 3° taper) | Single linear rectangular slot through head center |
|
Cam-Out Tendency
|
Near Zero (Straight square drive walls resist climbing) | Extremely High (Tends to climb up and out of slot under torque) |
|
Self-Holding 'Stick-Fit'
|
Yes (Taper friction-locks screw onto driver bit for horizontal/overhead 1-handed driving) | — |
|
Color-Coded Sizing System
|
#00 Orange, #0 Yellow, #1 Green, #2 Red (dominant wood/deck size), #3 Black, #4 Brown | — |
|
Primary Geographic Usage
|
Universal in Canada (electrical/framing/decking) / Pocket-hole woodworking globally (Kreg) | — |
|
Self-Centering Capability
|
— | None (Driver freely slides laterally out of slot) |
|
Power Tool Suitability
|
— | Unsuitable (High risk of workpiece scratching / bit slippage) |
|
Primary Modern Applications
|
— | Antique furniture restoration, electrical switch wallplates, plumbing fixtures |