Stemco Products Inc v. Atro LLC

I. Executive Summary and Procedural Information

• Parties & Counsel:
  • Plaintiff: Stemco Products, Inc. (Delaware)
  • Defendant: Atro, LLC (Delaware)
  • Plaintiff's Counsel: Husch Blackwell LLP
• Case Identification: 4:26-cv-00619, E.D. Mo., 04/27/2026
• Venue Allegations: Venue is based on Defendant Atro, LLC having a regular and established place of business in the Eastern District of Missouri and having allegedly committed acts of infringement within the district.
• Core Dispute: Plaintiff alleges that Defendant's "Steer King Universal Tie Rod" products infringe one utility patent and two design patents related to center linkage assemblies for heavy-duty trucks.
• Technical Context: The technology concerns tie rod assemblies, which are critical steering components that connect the wheel spindles of a vehicle, ensuring proper alignment and control.
• Key Procedural History: The complaint alleges that the accused product was developed with knowledge of the asserted patents, including through former Stemco employees now employed by Atro.

Case Timeline

Date	Event
2016-12-02	'905 Patent Priority Date
2017-01-30	'D283 Patent Priority Date
2017-01-30	'D305 Patent Priority Date
2019-07-09	'D283 Patent Issue Date
2019-10-08	'D305 Patent Issue Date
2022-07-26	'905 Patent Issue Date
2026-04-27	Complaint Filing Date

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 11,396,905 - Center Linkage Apparatus

• Issued: July 26, 2022

The Invention Explained

• Problem Addressed: The patent background describes the difficulty and time-consuming nature of properly installing center tube linkage assemblies on vehicle spindles. It notes that improper installation can lead to safety concerns and that different vehicle manufacturers use various spindle designs, complicating the process for technicians. U.S. Patent No. 11,396,905, col. 1:21-42
• The Patented Solution: The invention is a center linkage apparatus featuring tie rod ends that thread into a central component. The key innovation is a visual installation indicator: a "groove" is positioned on the threaded portion of the tie rod end. If this groove is visible to the installer, the component is not screwed in far enough; if the groove is hidden within the center component, it indicates a proper and secure installation. The patent also describes using opposite-direction threads for the two ends to prevent installing a tie rod on the wrong side of the vehicle. U.S. Patent No. 11,396,905, abstract U.S. Patent No. 11,396,905, col. 8:31-44
• Technical Importance: The patented solution aims to reduce installation errors and increase safety by providing a simple, unambiguous visual confirmation of proper assembly for a critical vehicle steering component. U.S. Patent No. 11,396,905, col. 3:31-34 U.S. Patent No. 11,396,905, col. 3:46-54

Key Claims at a Glance

• The complaint asserts infringement of at least independent Claim 1. Compl. ¶23
• The essential elements of independent Claim 1 include:
  • A center component with a hollow space and first and second threaded areas at opposing ends.
  • A first tie rod end component with a threaded surface to couple with the center component's first threaded area.
  • A "first groove" on the first tie rod end, adjacent to the threaded surface, "configured to indicate a first depth" of insertion into the center component.
  • A second tie rod end component with a threaded surface to couple with the center component's second threaded area.
  • A "second groove" on the second tie rod end, similarly "configured to indicate a second depth" of insertion.
  • The first and second tie rod ends are rotatable in opposite directions to couple with the center component.

U.S. Design Patent No. D853,283 - Center Link Assembly

• Issued: July 9, 2019

The Invention Explained

• Problem Addressed: Not applicable for a design patent.
• The Patented Solution: The 'D283 Patent protects the ornamental, non-functional design of a "center link assembly" as depicted in its figures. The claimed design consists of the visual appearance of the entire assembly, including the shape and configuration of the two end joints, the clamps, and the central connecting rod. D853,283 Patent, FIG. 1
• Technical Importance: Not applicable; its value lies in its distinct aesthetic appearance in the marketplace.

Key Claims at a Glance

• Design patents contain a single claim. The complaint asserts infringement of this claim: "The ornamental design for a center link assembly, as shown and described." Compl. ¶30

U.S. Design Patent No. D862,305 - Center Link Assembly

• Issued: October 8, 2019

The Invention Explained

• Technology Synopsis: This patent protects the ornamental design for a center link assembly. The claimed design, as shown in the patent's figures, is visually similar to the 'D283 Patent but is presented as a distinct embodiment, featuring break lines that suggest a component of indeterminate length. D862,305 Patent, FIG. 1 D862,305 Patent, FIG. 8
• Accused Features: The complaint alleges that the overall ornamental design of the Defendant's "Steer King Universal Tie Rod" is substantially similar to the design claimed in the 'D305 Patent. Compl. ¶41

Key Claims at a Glance

• Asserted Claims: The single claim for "The ornamental design for a center link assembly, as shown and described." Compl. ¶39

III. The Accused Instrumentality

Product Identification

The accused products are heavy-duty truck steering components marketed under the name "Steer King Universal Tie Rod," including at least models SKT-0967-MF and SKT-1080-MF (the "Accused Product"). Compl. ¶15

Functionality and Market Context

The Accused Product is designed to connect the spindles of opposing wheel ends on a truck's tractor or trailer. Compl. ¶16 The complaint states the product is marketed as delivering a "universal fit" and features "patent pending installation technology" intended to allow for faster installation and adjustment. Compl. ¶15 Plaintiff alleges the Accused Product is designed and marketed to compete directly with its own "QwikTie center link assembly." Compl. ¶16

IV. Analysis of Infringement Allegations

The complaint's specific element-by-element infringement allegations for the '905 Patent are detailed in a "Claim Chart attached hereto as Exhibit 4." Compl. ¶18 Compl. ¶23 As this exhibit was not provided, a claim chart table cannot be constructed from the complaint's narrative. The infringement theory is that the Accused Product practices, either literally or under the doctrine of equivalents, one or more claims of the '905 Patent, including at least Claim 1. Compl. ¶¶22-23

For the design patents, infringement is assessed under the "ordinary observer" test. The complaint alleges that the ornamental design of the Accused Product is "substantially similar" to the designs claimed in the '283 and 'D305 patents, such that an ordinary observer would be deceived into believing the products are the same. Compl. ¶32 Compl. ¶41 To support these allegations, the complaint provides visual evidence. The complaint includes a side-by-side comparison of a drawing from the 'D283 Patent and a photograph of the accused "Steer King Universal Tie Rod" Compl. p. 6 A similar side-by-side comparison is provided for the 'D305 Patent Compl. p. 8

Identified Points of Contention

• '905 Patent (Utility): The central dispute will likely concern the "groove ... configured to indicate a ... depth" limitation. A primary question for the court will be one of technical function: what is the nature of the Accused Product's "patent pending installation technology" Compl. ¶15, and does it include a feature that functions as a visual depth indicator in the manner claimed by the patent? Without details on the Accused Product's technology, the existence and equivalence of such a feature remains a key open question.
• Design Patents: The dispute will center on the overall visual appearance. A key legal question is whether an ordinary observer, familiar with prior art tie rods, would find the designs of the Accused Product and the patented designs to be substantially the same. The analysis will focus on the similarity of shape, configuration, and ornamentation, not on functional aspects or elements hidden from view during normal use.

V. Key Claim Terms for Construction

For U.S. Patent No. 11,396,905:

• The Term: "groove ... configured to indicate a ... depth"
• Context and Importance: This term appears to capture the core inventive concept of a visual aid for proper installation. The infringement analysis for the '905 Patent will likely hinge on how this term is construed and whether the Accused Product's "installation technology" falls within that construction.
• Intrinsic Evidence for Interpretation:
  • Evidence for a Broader Interpretation: The specification suggests the indicator is not limited to a literal groove, stating, "the apparatus can include a groove or a mark positioned on one or both of the first/second tie rod end components to indicate whether these components are properly installed." U.S. Patent No. 11,396,905, col. 3:55-59 This language may support a construction covering any visual marking that serves the indicating function.
  • Evidence for a Narrower Interpretation: The claim itself uses the specific word "groove." The primary embodiment shown in the figures and described in detail is a circumferential channel (414) that becomes physically "hidden" inside the center component upon proper installation. U.S. Patent No. 11,396,905, FIG. 4 U.S. Patent No. 11,396,905, col. 8:31-44 This may support a narrower construction limited to such a physical, concealable channel.

VI. Other Allegations

Indirect Infringement

The complaint focuses on allegations of direct infringement and does not plead specific facts to support separate counts for induced or contributory infringement.

Willful Infringement

The complaint alleges that Defendant's infringement has been and continues to be willful and deliberate. Compl. ¶26 Compl. ¶35 Compl. ¶44 The factual basis for this allegation is that the Accused Product was allegedly "developed with knowledge of Stemco's patent rights, including through former Stemco employees now employed at Atro who were aware of Stemco's patented QwikTie technology and intellectual property, including the Asserted Patents." Compl. ¶17

VII. Analyst's Conclusion: Key Questions for the Case

This case presents questions of both technical function and aesthetic design. The outcome will likely depend on the court's resolution of the following key issues:

• Technical Equivalence: Does the Defendant's "patent pending installation technology" function as a visual depth indicator in a way that falls within the scope of the '905 patent's claim term "groove configured to indicate a depth," either literally or under the doctrine of equivalents?
• Design Similarity: From the perspective of an ordinary observer in the heavy-duty truck parts industry, is the overall ornamental appearance of the "Steer King Universal Tie Rod" substantially the same as the aesthetic designs protected by the 'D283 and 'D305 patents?
• State of Mind: Can the Plaintiff prove its allegation that the Defendant had pre-suit knowledge of the asserted patents, particularly through former Stemco employees, which would be central to the claim for willful infringement and potential enhanced damages?