Definition
In aircraft hardware, a numerical designation indicating the diameter of a bolt, screw, rivet, or other fastener. For small fasteners, the size is typically expressed by a number (such as a #6 or #10 screw) that corresponds to a specific diameter in a standardized series. For larger fasteners, the size is given as a fractional or decimal measurement of the shank diameter.
Plain English
A standard way of describing how big a fastener is, usually by stating its diameter using a number from a recognized sizing system.
Context Anchor
Seen in aircraft fabric, wood, and surface-finishing work before paint or other protective coatings are applied.
Derivation
Size comes from an older finishing trade use of the word for a sealing preparation applied before the final surface coating. That helps separate it from the everyday meaning of size as how large something is.
Why Pilots Care
Using the wrong size fastener can cause loose joints, stripped threads, or structural failure. Maintenance technicians and pilots performing preventive maintenance must match fasteners exactly to the size specified in the maintenance manual.
Intuition Check
Do not read size here as the physical dimensions of a part. In this context, size means a sealing coating used before later finish coats.
Example Sentence 1
The maintenance manual called for a size 10 screw to secure the inspection panel.
Example Sentence 2
Pilots check runway length against the size category of their aircraft before landing.