A data transmission apparatus having first and second electrical conductors is disclosed. The first and second electrical conductors are disposed within recesses of a first and second complementary surfaces that are magnetically conducting and electrically insulating. The first and second surfaces are in close proximity to each other. The first surface is translatable along the length of the second surface. The first and second electrical conductors are in electromagnetic communication and provide for the transmission of data or power from the first electrical conductor to the second electrical conductor as the first surface overlaps the second surface. The data transmission apparatus may be located in one or more downhole tools.