Definition
The practice of using a tap or die to clean, straighten, or restore damaged or dirty threads on a bolt, screw, or threaded hole without cutting new threads. The tool follows the existing thread path to remove burrs, corrosion, paint, or minor distortion so the fastener can be properly torqued.
Plain English
Running a threading tool through an existing bolt or hole to clean up the threads so the fastener tightens correctly again. It tidies up the threads rather than making new ones.
Context Anchor
Seen in aircraft maintenance when a mechanic finds dirty, slightly damaged, or rough threads on a fastener or threaded fitting.
Derivation
Chasing' here comes from an old machinist's term for following or tracing along an existing path — in this case, following the existing thread groove rather than cutting a new one. The tool 'chases' the thread that's already there.
Why Pilots Care
Restored threads allow fasteners to achieve proper torque and clamping force, preventing loosening or failure in flight-critical components.
Intuition Check
Do not read “chasing” as pursuing something. In maintenance, it means following and cleaning up an existing thread path, not making a new one.
Example Sentence 1
Before reinstalling the cylinder, the mechanic spent a few minutes chasing threads on the case studs to remove old sealant.
Example Sentence 2
After removing corrosion from the wing attach bolts, the technician chased the threads to ensure smooth engagement during reinstallation.