Three conditions make a "set put up for retail sale", and one concept decides its code.
Is it a GIR 3(b) set at all?
A set must: (1) contain at least two different articles classifiable in different headings; (2) consist of items put together to meet a particular need or carry out a specific activity; (3) be packed for direct sale to users without repacking. Fail any limb and each item is classified separately — which is often the better outcome, and sometimes the trap.
Essential character
The set follows the component that gives it its essential character: by value, bulk, weight, role in use — no fixed formula, judged case by case. A manicure set in a leather case follows the manicure tools, not the case (GIR 5 covers the case). A drone with a spare camera may follow the drone; a camera bundled with a drone accessory may not.
When 3(b) fails: 3(c)
If no single component predominates, the set goes to the heading last in numerical order among those competing — a mechanical tie-breaker that surprises people ("why is my food gift box classified as the chocolate?").
Documentation that wins disputes
Keep a bill of materials with values per component, photos of the retail packaging, and a one-paragraph essential-character argument. US CROSS and EU BTI databases are full of set rulings — cite the closest ones.
E-commerce angle
Bundles created at the fulfilment center AFTER import are not import "sets" — each component was classified separately at entry. Conversely, breaking a factory retail set into components on the invoice to lower duty is misdescription. Structure the bundle before the invoice is issued, not after.