Internally latched subsea wellhead tieback connector

The connector 10 has an axially movable lock ring operating hydraulic piston 36 and an inner body 18 carrying an axially adjustable expanding lock ring 28 by means of a threaded adjustment ring 30, and a reaction ring 32. The ring 28 is axially adjusted so that it can enter a groove in a wellhead 14 with axial preload to stretch the connector 10. The piston end 22 engaging the ring 28 and the ring have facing raduissed ends to create an enhanced mechanical advantage to originate a required pre-load force without the necessity of having to generate a large hydraulic force that would otherwise be needed. The ring 30, the piston end 22 and the inner body 18 aid pre-load force generation by deflection.