Hex / Allen vs. Robertson
Comparing 2 standards across 9 specifications. 9 key differences identified.
The Hex drive (Allen socket / Internal Hexagon, standardized under ISO 4026 and DIN 912) is a 6-sided symmetrical polygonal drive recess developed in the early 1900s by William G. Allen. Widely used in socket head cap screws, bicycle components, and flat-pack furniture, it provides high clamping torque with compact cylindrical head profiles.
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.
Specification Comparison Table
9 Parameters| Parameter / Spec | ||
|---|---|---|
|
Standard Specifications
|
ISO 4762 / DIN 912 (Socket head cap screws) / ASME B18.3 | CSA B35.4 / ANSI Type III Square Recess / ASME B18.6.3 |
|
Drive Geometry
|
Symmetrical 6-sided internal hexagon socket | 4-sided square recess with a slight interior conical taper (approx. 3° taper) |
|
Cam-Out Tendency
|
Low (Requires axial insertion depth; strips if bit is worn or undersized) | Near Zero (Straight square drive walls resist climbing) |
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Metric Standard Sizes
|
1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0, 12.0, 14.0, 17.0 mm | — |
|
Imperial Standard Sizes
|
0.050", 1/16", 5/64", 3/32", 1/8", 5/32", 3/16", 1/4", 5/16", 3/8" | — |
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Primary Applications
|
Machine tools, bicycle components (4/5/6mm), 3D printers (2.5/3mm), flat-pack furniture | — |
|
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 |
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Primary Geographic Usage
|
— | Universal in Canada (electrical/framing/decking) / Pocket-hole woodworking globally (Kreg) |