A Merlin™ family mechanical connector provided with a thread on substantially matching frustoconical surfaces extending between two sets of nipple seals utilize assembly/disassembly fluids that solidify after the assembly and are brought to liquid state before the disassembly. They include resins or tar-like non-metals and liquid metals solidifying in single phases as well as in multiple phases like for example binary, ternary etc. eutectics. That improves already very good leak resistance of Merlin™ family connectors and benefits good heat transfer between pins and boxes. Thread angle mismatching between box and pin threads can be introduced in order to improve loading. The above modifications can be introduced to traditional connectors featuring torsional load capacities limited to frictional resistance and to connectors designed to transfer high torsional loads.