second nesting stem 16 and passing through aperatures 30 and each connecting to and terminating at the electrical leads 24 when the first nesting stem 2 and the second nesting stem 16 are joined the second nesting stem 2 is turned down on the first nesting stem 16 and the metal contacts 15 intimately touch metal contacts 28 thus completing the conduit from metal leads 7 to metal leads 24 the compression spring 25 ensures that this contact is maintained in use a roof structure is provided with a roof deck and a water impermeable membrane is laid down over the roof deck the roof deck and membrane can be premeasured and premarked for installation points at which the devices of this invention are secured but it is normal practice to install the roof piecemeal after the water impermeable membrane is laid down and therefore the size of the thermal insulation planking or the size of planking on the top most layer can determine the installation points of the device since the device is designed to be installed where the four corners of the top planks intersect so that the top plate 18 of the device can grip the corners of the top most planks and hold them down or the devices can be installed such that the device holds down the center of the top planks by whatever procedure desired the enlarged flange base 1 containing the first nesting stem 2 and the hub 10 integrally secured thereto is first securely fastened to the roof deck over top the water impermeable membrane using a mechanical fastener such as a bolt screw or nail.