filing vs metal filing

filing and metal filing both are nouns.

Word	Noun	Adjective	Verb	Adverb
filing	Yes	No	No	No
metal filing	Yes	No	No	No

As nouns, metal filing is a hyponym of filing; that is, metal filing is a word with a more specific, narrower meaning than filing:

filing (noun)	metal filing (noun)
preservation and methodical arrangement as of documents and papers etc.	a fragment of metal rubbed off by the use of a file
the act of using a file (as in shaping or smoothing an object)
the entering of a legal document into the public record
a fragment rubbed off by the use of a file