Abstract: An apparatus for use with an oil well drilling apparatus, including an annular spool interposed permanently between the well blowout preventer stack and the upper bell nipple. The spool receives a plurality of different mandrels, including a test mandrel for testing the seals of the blowout preventers or adapting the drilling apparatus for wireline operations, and a shut-down mandrel for suspending a string of drill pipe within the well casing during a temporary shutdown. The different mandrels are each seated on an internal annular seat in the spool, are each peripherally sealing in the spool above the seat, and are retained by appropriate securing means urging the mandrel against the spool seat.