Sorry - 'hit the nail on the head'. Literally: (you touched == tetigit (tangere)) ([the] point == rem (res)) (with [a] needle == acu (acus))'.[0] 'Point' (res) is already abstract - 'matter', 'thing' - not being used figuratively like the rest of the phrase.

It's one of those phrasoids which is permanently stuck in my head from Latin classes when I was a teenager, but I might've been wrong in thinking it was one of the more widely-recognised ones.

[0] 'You' is implied by the second-person verb ending on 'tetigit', 'with' is implied by the ablative case ending on 'acu' (the 'ablative of means'), while 'the' and 'a' are filled in altogether since Latin has no concept of definite/indefinite articles.