noun
teeth of a rasp; file teeth
Refers to the individual cutting teeth on a rasp or file.
このやすりはやすり目が細かいので、仕上げに適している。
This file has fine teeth, so it's suitable for finishing work.
noun
rasped area; filed surface
Refers to the area or surface that has been rasped or filed.
金属のやすり目を滑らかにするために、さらに細かいやすりをかけた。
To smooth the filed area of the metal, I used an even finer file.
やすり is the tool itself (a file or rasp), while やすり目 refers specifically to its teeth or the surface left by filing.
Compound of やすり (rasp/file) and 目 (eye, here meaning 'pattern' or 'texture'). The exact origin of やすり is uncertain, but it may be related to the verb やする (to smooth).