Tamper-Resistant Fastener With Ellipsoidal Post
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Solution Overview
Problem
Existing tamper-resistant fasteners with cylindrical center posts are vulnerable to unauthorized removal, as they do not transmit torque effectively and can be compromised by drilling, while authorized removal often damages the fastener.
Innovation Solution
A fastener design featuring a non-circular, ellipsoidal recess combined with an elongated, ellipsoidal center post that aligns with the recess, allowing for uniform torque distribution and making unauthorized tool fabrication more difficult.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cylindrical center post is used in a recessed drive socket, then the fastener provides some tamper resistance, but the center post does not transmit torque effectively and can be compromised by drilling a hole through it
Solution Approach 1:
The patent changes the center post from a cylindrical symmetric shape to a non-circular asymmetric shape that matches the recess profile (hexagonal, TORX®, Bristol, Phillips, or custom profiles). This asymmetric design prevents unauthorized tools from effectively engaging the post while allowing the authorized driver to transmit torque through both the recess walls and the post, resolving the contradiction between tamper resistance and torque transmission.
2Device complexity
If a cylindrical center post is used, then the fastener structure is simple, but authorized persons cannot remove the fastener without resorting to crude methods that mutilate the fastener
Solution Approach 1:
The non-circular center post design maintains relatively simple manufacturing while enabling authorized removal through a matching driver. The asymmetric profile allows the authorized driver to engage both the recess and post for controlled removal, whereas unauthorized attempts with conventional tools or drilling methods will mutilate the fastener, thus resolving the contradiction between structural simplicity and ease of authorized operation.
3Ease of manufacture
If the center post is cylindrical, then manufacturing is simple, but a determined thief can fabricate a tool by drilling a hole through the center of a conventional driver
Solution Approach 1:
The patent employs a non-circular center post with profiles matching standard recess types (hexagonal, TORX®, Bristol, Phillips) or custom designs. This asymmetric geometry maintains manufacturability through standard machining processes while preventing thieves from successfully fabricating bypass tools, as drilling through conventional drivers will not clear the non-circular post without damaging the driver's outer walls. This resolves the contradiction between ease of manufacture and reliability of anti-tamper features.
4Device complexity
If only the recess walls carry the applied torque, then the fastener design is simpler, but a greater torque cannot be applied compared to when the center post also engages
Solution Approach 1:
The patent merges the torque transmission function into both the recess walls and the center post by designing the post to engage with the authorized driver. This dual engagement path allows torque to be distributed across both components, enabling greater torque application without increasing overall design complexity, thus resolving the contradiction between device simplicity and torque capacity.
Data Source
AI summary
A tamper-resistant fastener includes a non-circular drive recess optionally with a non-circular center post. Preferably the recess and center post are at least partially ellipsoidal cylinders that are concentric and aligned (i.e. they share a common major axis direction). This configuration forms a slot having preferably a substantially uniform width into which an authorized driver is inserted. The length of the major maximum dimension of the post is selected so that a circular arc tangent to the maximum radius of the post will pass closely to or intersect the minimum radial dimension of the recess.