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Start with a drawing and the mating tube
A useful enquiry shows how the cap fits the tube. Include a drawing or a clearly labelled sketch, the drawing revision and the measurement units. Identify whether the quoted diameter refers to the cap inside diameter, cap outside diameter or the mating tube.
A shorthand size pair can be a starting reference, but it does not define the complete part. Confirm the meaning of each value before selecting a component.
Confirm depth, wall thickness and tolerances
For a custom cap, specify the required depth as well as the wall thickness. Mark the dimensions that affect assembly and explain whether your application needs an insertion depth or an overall height.
If depth is absent from a catalogue listing, request confirmation against the drawing. Do not infer it from diameter or wall thickness. Provide the intended fit and dimensional tolerances so the supplier can review the requirement.
State material and joining requirements
Include the copper grade and material condition you require, together with any surface or cleanliness requirements. Explain the intended joining process and operating conditions where these affect selection.
Material certificates, dimensional inspection and application ratings should be agreed in the order documents. A product photograph alone cannot establish those requirements.
Complete the commercial enquiry
Add the order quantity, expected repeat demand, delivery destination and packing requirements. Attach any inspection checklist or sample reference available to your team.
Before ordering, ask for a quotation that refers to the agreed drawing revision, material and inspection scope. This gives both parties a clear basis for production and acceptance.