Check the external threads of the screw: If the threads show obvious wear, deformation, or chipping; or if the thread crests are flattened into a smooth, "toothless" surface, the screw can basically be determined to be stripped.
Check the screw head: Wear or slipping in the drive recess (such as Phillips, slotted, or hexagon socket) — where the tool fails to engage securely during turning — is also regarded as stripping in a broad sense (referred to as head stripping).
Check the matching nut/threaded hole: For screws installed in nuts or pre-tapped holes, inspect the inner wall of the threaded hole for thread deformation or detachment. Residual plastic debris is also a sign of thread damage.
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No-load turning test
Unscrew the fastener from the threaded hole/nut and feel the resistance. If turning requires no resistance at all, or if the resistance fluctuates sharply with a "spin-free" sensation, it indicates thread engagement failure and confirms stripping.
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Tightening resistance test
A normal plastic screw will exhibit a noticeable progressive increase in resistance when tightened to a certain point. A sudden loss of resistance during tightening, or the screw spinning indefinitely without achieving further clamping force, is a classic sign of stripping.
A properly tightened plastic screw will hold the two components firmly in place without any looseness.
If the fastened components still wobble or shift after the screw is fully tightened, or if the screw loosens with a light twist — even if there is no visible wear — it means the thread engagement is insufficient, indicating hidden stripping.
