the unwritten rule of senatorial courtesy applies to what appointments
Senatorial courtesy Senatorial courtesy is a long-standing unwritten, unofficial, and nonbinding political custom (or constitutional convention) in the United States describing the tendency of U.S. senators to support a Senate colleague in opposing the appointment to federal office of a presidential nominee from that Senator's state.[1] The practice is motivated by a general sense of collegiality among Senators and the assumption that a Senate colleague will have the best first-hand knowledge of the personal character and qualifications of nominees from his or her own state. It is also viewed as an "important source of political patronage"[2] for U.S. senators.
United States congressional conference committee The authority to appoint conferees lies in the entire House, and the entire Senate can appoint conferees by adopting a debatable motion to do so.[3] But leadership have increasingly exercised authority in the appointment of conferees.