A pressurization tool comprises a body for connection to a tubular by box, and pin, and providing for flow of fluid by way of a throughbore of varying cross-section to form chambers. A lower chamber accommodates a spring that contacts a shoulder providing a reaction surface for compression of the spring under applied force. The chamber merges into intermediate chamber that accommodates a movable index sleeve that cooperates with an index pin inserted through the wall of the tool body. Associated with the upper part of the index sleeve is a valve seat assembly, positioned to abut the index sleeve and moveable therewith, said valve seat assembly being configured to receive a plug or ball, and in one unpressurised configuration, is located in a wider chamber that permits fluid flow around the assembly.