Work from a drawing, from a sample, or from a failed part where no drawing survives. Material identified before cutting where the original spec is unknown. Fits machined to the actual mating component rather than to a nominal dimension.
Obsolete thread forms and non-standard tapers cut to the existing mate. Single-billet jobs sequenced so an error doesn't cost the material. Blanks produced in-house when the section isn't available as stock.
