like a square tenon for a round mortice (/a round peg in a square hole)—at variance with each other
❍ 持方枘欲内圆凿，其能入乎？(《史记·孟子荀卿列传》) How can you fit a square peg into a round hole?
方枘圆凿圆凿方枘fānɡ ruì yuán zuò
凿：榫眼；枘：榫头。方榫头插不进圆榫眼。比喻不相投合。at variance with each other, like a square tenon for a round mortise, a square handle and round socket