Where did you find the 7 character suggestion? 7 used to be the default suggestion, but the problem of collisions has been acknowledged and dealt with by the git project. Linus himself authored the change that made the abbreviated revision length vary based on the size of the repository: https://github.com/git/git/commit/e6c587c733b4634030b353f402.... Also, the command for creating references to other commits which comes from the git project and is linked to in the article also uses automatic abbreviation length.