Shop description of a fastener that has yielded and begun to concentrate its stretch in one place, showing a waist in the threads or shank and often threads with an uneven, stretched pitch that will not take a nut freely. A necked bolt has lost its spring and is close to breaking, so it goes in the scrap bin. Running a nut down the full thread by hand is the quick shop check.
Every one of these head bolts is necked down in the middle, you can see light under the straightedge, bin them.
Also heard as
- necked
- stretched
- necking
Related terms
Torque-to-yield
Tightening by torque plus angle until the bolt just yields, giving consistent high preload; the bolt is single-use.
Bolt stretch
The elastic elongation of a bolt under preload, measured directly as the most accurate check of tension.
Twisted off
Describes a bolt or screw that snapped in torsion while being tightened or removed, leaving the stub behind.