a peg to hang a matter on

a peg to hang (something) on

Something that functions largely or primarily in service of expressing or presenting something else, often one's opinions, beliefs, or ideas (about something). Because of the persistent (but incorrect) notion that one shouldn't end a sentence in a preposition, some writers prefer the form "a peg on which to hang (something)." It become clear from very early on that the director is using this adaptation as a peg to hang his own political agenda on. The musical is primarily a peg on which to hang a plethora of catchy, upbeat song-and-dance numbers, so most audiences will likely be willing to forgive its laughably thin story.
See also: hang, on, peg
Farlex Dictionary of Idioms.

a peg to hang a matter on

something used as a pretext or occasion for the discussion or treatment of a wider subject.
See also: hang, matter, on, peg
Farlex Partner Idioms Dictionary
See also:
  • a peg on which to hang (something)
  • a peg on which to hang something
  • a peg to hang (something) on
  • a peg to hang something on
  • a ghost at the feast
  • (you've) got to get up pretty early in the morning to (do something)
  • a/the feel of (something)
  • (I) wouldn't (do something) if I were you
  • (one) could use (something)
  • all righty