Definition
The length of the unthreaded, smooth shank of a bolt — measured from under the head to the start of the threads. In aircraft assembly, the grip length should match the combined thickness of the materials being joined so that the bolt's shank, not its threads, passes through the load-bearing holes.
Plain English
The smooth part of a bolt between the head and the threads. When you pick a bolt for a job, this smooth section needs to be about as long as the parts being bolted together are thick.
Context Anchor
Seen in aircraft maintenance, structural repair, and hardware selection when choosing the correct rivet or bolt for a joint.
Derivation
Grip' comes from the Old English 'gripan,' meaning to grasp or hold firmly. The grip length is the part of the bolt that 'grips' the materials being joined — holding them tightly with smooth shank rather than threads.
Why Pilots Care
Correct grip length keeps threads out of the load-bearing area, preserving full shear strength and preventing fatigue failure.
Analogy
Think of fastening a stack of papers with a binder clip. The clip has to fit the thickness of the stack; too small or too large, and it will not hold properly.
Intuition Check
Grip length does not mean how much of the fastener you can grab. It means the thickness of the material the fastener must hold together.
Example Sentence 1
The mechanic measured the combined thickness of the two fittings and chose a bolt with a matching grip length.
Example Sentence 2
Using a bolt with too short a grip length placed threads inside the spar web and reduced the joint strength.