noun
metal bars of a kendo face guard
Refers specifically to the metal grill that protects the face in kendo armor (面).
面がねが歪んでしまったので、新しいものに交換した。
The metal bars of my face guard got bent, so I replaced them with new ones.
面 is the entire kendo face mask, while 面がね specifically refers to the metal grill portion.
Compound of 面 (めん, 'face mask') and 金 (かね, 'metal'), with rendaku voicing of かね to がね.