Definition
A coil spring whose two ends are joined to form a continuous ring, used to apply uniform inward radial pressure around a shaft. In aircraft engines and accessories it is most commonly fitted inside the lip of an oil seal, where it keeps the sealing lip pressed evenly against the rotating shaft to prevent oil leakage.
Plain English
A small spring shaped like a coiled loop that forms a closed circle. It sits inside the rubber lip of an oil seal and gently squeezes inward all the way around, holding the seal tight against a spinning shaft so oil cannot escape.
Context Anchor
Seen in aircraft engine maintenance when inspecting or installing oil seals around rotating shafts.
Derivation
Circumferential means 'around the outside edge,' from the Latin circum (around) and ferre (to carry). Garter refers to the elastic band once worn around the leg to hold up a stocking — same idea here: a continuous loop that grips evenly all the way around.
Why Pilots Care
If this spring is missing, damaged, or out of place, the seal may not press firmly enough against the shaft, which can lead to oil leakage and engine maintenance problems.
Analogy
Think of the elastic band sewn into the cuff of a sleeve. It pulls the fabric snug against the wrist no matter how the arm moves. The garter spring does the same job for a seal lip against a turning shaft.
Intuition Check
Do not picture a straight spring that pushes from one end. A circumferential coil spring works in a circle, holding even pressure around the seal.
Example Sentence 1
When replacing the crankshaft oil seal, the technician inspected the garter spring to make sure it had not stretched or come unhooked from its loop.
Example Sentence 2
Inside the magneto the garter spring maintains steady pressure so the brushes stay in contact with the commutator.