A specification has two jobs: let a supplier price the work, and let both sides agree later on whether the result is correct. Most documents do the first badly and the second not at all.
Make every requirement testable
« High quality finish » cannot be measured, so it cannot be enforced. « No visible tool marks on surfaces A and B, inspected at 50 cm under office lighting » can. The second version costs nothing extra to write and settles an argument that would otherwise happen after the container lands.
What belongs in the document
- Dimensions with tolerances — and which ones are critical rather than nominal.
- Materials by grade and standard, not by common name.
- The finish, with an inspection condition attached.
- Packaging, because it is a real cost and a real source of damage.
- What must be tested, by whom, and what a failure means.
Say what can change
Chinese manufacturers are often better than their customers at knowing which tolerance is expensive and which is free. A specification that marks its own flexibility — « this radius is cosmetic, this one is functional » — invites suggestions that lower the price without lowering the product.
Have it read back to you. Ask the supplier to describe what they will make, in their words. Any gap between their description and your intention is a defect you have just avoided paying for.