Aro Manufacturing Co. v. Convertible Top Replacement Co.
The Supreme Court ruled that a car owner who replaces a worn-out convertible top fabric is not infringing the patent covering the whole top assembly, because the fabric itself was never separately patented.
The decision means companies that sell replacement parts for patented products generally cannot be sued for patent infringement just because their part fits into a larger patented combination, so long as the part itself isn't separately patented and buyers are simply repairing, not rebuilding, the product.
“We hold that maintenance of the “use of the whole” of the patented combination through replacement of a spent, unpatented element does not constitute reconstruction.”
The Court's core holding that replacing a worn-out part is repair, not infringement.
How it got here: A trial court found the patent valid and infringed, the Court of Appeals affirmed, and the Supreme Court agreed to hear the replacement-fabric maker's appeal.
The Case in Depth
What happened
A company that manufactures replacement convertible-top fabrics sold fabric covers designed to fit cars whose original tops used a patented sealing mechanism. The patent holder, which had acquired rights to that patent for Massachusetts, sued the replacement-fabric maker and its officers, claiming that selling these fabrics helped car owners illegally recreate the patented top once the original fabric wore out after a few years of use.
The question before the Court
When the fabric top on a convertible car wears out, can the car owner buy a replacement fabric without the patent holder's permission?
The Court's answer
No — the Supreme Court ruled that replacing a spent, unpatented fabric top on a patented convertible-top assembly is permissible repair, not infringement. Since the fabric itself was never separately patented, and a combination patent only protects the whole assembled combination (not any single unpatented part within it), the car owner does not directly infringe by swapping in a new fabric top, no matter how central that fabric was to the invention.
Because there was no direct infringement by the car owner, there could be no contributory infringement by the company that manufactured and sold the replacement fabrics either. The Court rejected tests based on a part's cost, durability, or importance to the invention, holding that such factors wrongly treat an unpatented component as though it carried its own separate patent protection.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
Businesses that manufacture replacement parts — for cars, machines, or any product built from a patented combination of ordinary components — can keep selling those parts without fear of patent liability, as long as customers are just fixing worn-out products rather than building new ones. Consumers benefit from a competitive market for replacement parts rather than being locked into buying only from the original patent holder.
What changes now
This is a final decision on the merits reversing the Court of Appeals, so the injunction against the replacement-fabric maker is undone and the damages proceeding before the court-appointed master is no longer supported. The ruling establishes that selling unpatented replacement components for patented combinations, without more, does not amount to patent infringement, a rule other manufacturers and courts will apply going forward in similar repair-versus-reconstruction disputes.
What this does not decide
The Court did not decide whether entirely rebuilding a spent patented combination from scratch, or replacing a part that is itself separately patented, would also be permissible. The ruling is limited to unpatented components being swapped in as ordinary repair, not to wholesale reconstruction of a used-up device.
Concurrences and dissents
How the Justices voted
Majority (1). Justice Whittaker (author).
Separate writings (2). Justice Black (author of a concurrence).
Dissent (1). Justice Harlan (author).
Concurrence — Justice Black
Justice Black agreed fully with the majority's reasoning but wrote separately to reject the multi-factor tests proposed by Brennan and Harlan as unnecessarily confusing. He argued the real question is simply whether the owner 'made' a new patented article, and warned that vague standards would expose small businesses to crippling treble-damages liability for selling ordinary replacement parts. Read the full concurrence →
Concurrence — Justice Brennan
Justice Brennan agreed the fabric replacement was repair, not reconstruction, but rejected the majority's bright-line test as too narrow. He argued courts should weigh multiple factors—part lifespan, cost, importance to the invention, and the parties' understanding—and would have made an independent factual determination rather than deferring to the lower courts, reversing except as to certain Ford-related relief. Read the full concurrence →
Dissent — Justice Harlan
“he may not, without rendering himself liable for infringement, reconstruct the device itself”Harlan's statement of the traditional rule distinguishing permissible repair from forbidden reconstruction.
Justice Harlan argued the majority's rule was too rigid, departing from a century of case law holding that reconstruction versus repair depends on multiple factors specific to each case, not just whether a component is separately patented. He would have deferred to the two lower courts, which had applied the correct multi-factor standard and found contributory infringement, and would have affirmed. Read the full dissent →
How the Court got there
The legal reasoning, step by step
- The Court first established that a combination patent — one covering only the assembled combination of parts, not any single part — gives the patent holder no monopoly over any individual unpatented component, however essential that component is to making the combination work.
- Because contributory infringement (helping someone else infringe) cannot exist unless there is also a direct infringement by the actual user, the Court had to decide whether a car owner directly infringes the patent by replacing the worn-out fabric top.
- Drawing on the long-standing distinction between permissible 'repair' and forbidden 'reconstruction,' the Court explained that an owner who buys a patented item buys the right to keep using the whole of it, including replacing parts that wear out, so long as the owner isn't essentially building a brand-new patented item from scratch.
- The Court rejected the lower courts' approach of weighing factors like how expensive, durable, or central to the invention a part is, holding instead that such factors improperly treat an unpatented component as if it had its own separate patent protection.
- Applying this rule, the Court concluded that swapping in a new fabric top — one worn-out part among several unpatented parts — is ordinary repair rather than a second creation of the patented combination, so no direct infringement, and therefore no contributory infringement, occurred.
Doctrinal impact
Cases affected by this decision
Reaffirms Mercoid Corp. v. Mid-Continent Co. (320 U.S. 661)
Relied on for the rule that no single element of a combination patent is separately protected.
Reaffirms Wilson v. Simpson (9 How. 109)
Treated as the authoritative case allowing replacement of worn-out parts without infringing.