noun
gudgeon; hinge knuckle
Technical term in hardware and carpentry; refers to the socket or eye part of a hinge into which the pintle fits, or a similar pivot component.
この扉のつぼ金が摩耗して、開閉時にきしむ音がする。
The gudgeon on this door has worn down, causing a creaking sound when opening and closing.
つぼ金と軸受けの隙間を調整してください。
Please adjust the clearance between the gudgeon and the bearing.
蝶番 is the general term for a hinge, while つぼ金 specifically refers to the knuckle or gudgeon part of a hinge.
Compound of つぼ (likely referring to a socket or hollow part) and 金 (metal). The exact derivation is uncertain, but the term is conventionally associated with metal hinge components.