From Longman Dictionary of Contemporary Englishthe nuts and bolts of somethingthe nuts and bolts of somethinginformalDETAIL the practical details of a subject or job the nuts and bolts of government → nut
Examples from the Corpus
the nuts and bolts of something• That meant that they could not stand the Central Office youths involved in the nuts and bolts of the campaign.• He did pioneering work in figuring out the nuts and bolts of sustainability.• They're good guys, but I'm not sure how familiar they are with the nuts and bolts of the banking system. 