Casting that is identical with the first article for the most aspects but was not or only partly produced using the equipment and processes that are applied for series production.

The supply of prototypes may be agreed between the purchaser and the manufacturer. In case that prototypes are only used for dimensional inspection, whereas the material properties of the prototype are allowed to deviate from those agreed for series parts, this condition must be specifically agreed between the manufacturer and the purchaser.

In the event that the agreed clearances and tolerances are exceeded by the prototype, new limits and tolerances may be agreed, provided that the purchaser can obtain approval for any such deviations. Preliminary agreement of acceptance criteria and conditions, as well as documentation of such agreements in the contract is recommended.

Additional references:
Acceptance certificate
Acceptance inspector
Factory certificate
Sample casting
First article inspection
Subsequent sampling

Literature references:
EN 1559-1, Founding, Technical conditions of delivery - Part 1: General