The answer is outliners. Milady's definition matches the question directly: outliners, also known as trimmers or edgers, are essential tools for finish and detail work.
Elsewhere the book adds that outliners are essential for detail, precision design, and fine finish work on haircuts and facial hair trims, including the eyebrows. Detachable-blade and adjustable-blade clippers are real, separate clipper categories used for the bulk of a haircut, not the fine detail work this question is asking about.
Milady Standard Barbering, 6th ed., Ch. 5 (Implements, Tools, and Equipment), p. 114: "Outliners, also known as trimmers or edgers, are essential tools for finish and detail work."
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