Definition
A slender wire nail with a small, slightly tapered head, used in aircraft woodwork where the head must sit flush with or just below the surface of the wood without splitting it.
Plain English
A thin nail with a small head, designed to be driven into wood so the head almost disappears into the surface.
Context Anchor
Seen in maintenance, repair, or restoration work on fabric-covered aircraft with wooden parts.
Derivation
The word 'casing' comes from the Old French 'casse,' meaning a frame or container. In carpentry, 'casing' refers to the trim around a door or window frame -- the kind of finish work where a small, low-profile nail head is desirable. The nail took its name from that use.
Why Pilots Care
On wooden aircraft and during fabric covering work, the right fastener matters. A casing nail holds securely without splitting thin wood members and leaves a clean, low surface that won't snag fabric or interfere with a smooth finish.
Intuition Check
Do not read casing here as engine casing. A casing nail is a type of small nail used in covering or woodwork, not a nail for an engine case.
Example Sentence 1
The mechanic used casing nails to attach the fabric reinforcing tape to the wooden wing rib.
Example Sentence 2
After driving the casing nails flush the wood surface remained smooth for the final varnish coat.