significantly torqued one into the other while maintaining an annular separation and therefore electrical separation as part of the assembly procedure the co joined coaxial cylinders can be placed into an injection moulding machine wherein a high performance thermoplastic is injected into the annular space thereby forming both an insulative gap and a strong joint between the cylinders in the newly created em gap sub application_number US 201113087020 A description fig1 is a simplification of a typical drilling rig employing an em telemetry method of transponding drilling parameters from downhole to surface the derrick 1 supports and drives the jointed pipe drill string 2 that is required to drill a well the drill string comprises a number of tubular members drill pipes 3 and a bottom hole assembly bha 4 the bha 4 in this embodiment comprises an em gap sub and telemetry device 5 a mud motor 6 and a drill bit 7 as the mud motor 6 rotates the drill bit 7 and the well progresses it is necessary to record various drilling parameters to help the driller safely guide the well these parameters are gathered and encoded onto an em carrier that is electrically produced across the insulation gap 8 of the em gap 5 a tiny fraction of this signal is detected at the surface by the measuring the signal formed between the rig 39 s derrick 1 and a surface antenna 9 located in.