Definition
A machinist's measuring tool consisting of a graduated steel rule used with three interchangeable heads: a square head (for measuring 90° and 45° angles and as a depth gauge), a protractor head (for measuring any angle), and a centre head (for locating the centre of a round bar). Used in aircraft maintenance and sheet-metal work for layout and inspection.
Plain English
A toolkit built around a steel ruler that can have three different attachments slid onto it, letting one tool measure right angles, any angle, and the centre of round stock.
Context Anchor
Used in aircraft maintenance shops during measuring, layout, fitting, and marking work before cutting, drilling, or assembling parts.
Derivation
Called a 'combination set' because one rule combines with several heads to perform the work of several separate tools. The name describes the kit, not any single piece.
Why Pilots Care
Accurate measuring and marking help aircraft parts fit correctly. A small layout error can lead to a misplaced hole, poor fit, or a part that must be remade.
Intuition Check
Do not read “combination set” as a general kit of mixed tools. In maintenance, it means one measuring rule used with several specific heads.
Example Sentence 1
The mechanic used the protractor head of his combination set to check the angle of the bracket before drilling.
Example Sentence 2
Before drilling the new spar web, she marked the rivet line with the combination set to keep the spacing uniform.