The F5 dual-frequency transmitters (Model HDT) come in two configurations:  19.2 kHz/12 kHz and 12 kHz/1.3 kHz.  These transmitters have light-green tubes and incorporate the new mechanical design like that used for the fluid pressure transmitters.  The new design has a knurled battery cap that is not flush with the battery compartment, as the older version was.  With the cap installed, the overall length is still 15 in. (38.1 cm), but without the cap the length is 14.6 in. (37.08 cm).  Thus, the HDT transmitters are compatible with existing drill housings that accommodate 15 in. (38.1 cm) DigiTrak transmitters. If using a tooling adapter, however, the new design will require a different adapter.