There are very few "formal" specifications for a T-TRAK module, however, if those few specifications are followed, all T-TRAK modules are compatible with each other.

In a nutshell:

Module Height - adjustable between 70-100mm ( 2.75" & 4.0")

Module Length - 308mm (12 1/8") (310mm of track)

Kato Unitrack at the module interfaces/track spacing of 33mm

Track offset from front facia - 38mm (1.5") to edge of ballast

Electrical connections - BWWB (blue, white, white, blue) using Kato connectors

In order to begin the conversation on standards some definitions must be established. The "length or width" of the module is the axis parallel to the track. The terms length and width are used interchangeably in T-TRAK. The "depth" of the module is the dimension perpendicular to the track and is the distance from the front (nearest the track) of the module to the back. The "height" of the module is measured from the bottom of the module to the base of the track.

The first item in the list of formal T-TRAK specifications is that the track at the module edges must be Kato Unitrack. Modules in a layout are not clamped or bolted together in any fashion. The only thing that holds the modules together in a layout are the the Kato unijoiners. It is acceptable to use track from other manufacturers between the Kato Unitrack interfaces, however, most T-TRAK builders use Kato Unitrack exclusively on their T-TRAK modules. The use of Kato track created an early "informal" standard for the length of track on a module to be 310mm. A module of this size is typically referred to as a "single". A module with 620mm of track is referred to as a "double". Naturally, those with 930mm of track are known as "triples". Since Kato track is measured in metric units it is easiest to build modules using metric measurements. 

There are multiple ways to build a T-TRAK module but the most common is the box method. This is basically a lidless, inverted box. For a module of single length the box should be no more than 308mm (12 1/8") wide. This gap provides for 1mm of track overhang on each side of the module. This 1mm overhang is part of the formal T-TRAK standards. It was implemented to allow flexibility with connecting to other modules that may not be built squarely, or for those that warped or flexed. The formal standard height of the module is 70mm (2¾") and is adjustable to a height of 100mm (4") by utiliizing leveling bolts. The height measurement is from a flat surface to the base of the Kato track. There is no formal specification for the depth of a module. The general consensus among the T-TRAK community is that a module should be no deeper than 355mm (14").

The track placement standard for T-TRAK modules is a bit unique and is an outcome of the use of Kato Unitrack. The formal offset from the front fascia to the edge of the ballast of the front track is 38mm (1 1/2"). Track spacing of 33m is the most common spacing for existing modules and is identical to Kato's double track pieces. It is best to use Kato's double track sections as alignment tools when affixing track to a module.

Electrical Standards

The wiring specification is a formal standard. For modules wired for track power and using standard Kato connectors, the specification is that the rails, beginning with the front rail on the front track, be wired in a Blue, White, White, Blue order. This is also known as "blue to the outside". The proper way to reverse the polarity for the inner line is to do so at the power pack and not at the module. All modules that feature a power drop should be wired to the specification and have the Kato power connectors. It is best to have a power drop every six to eight single modules (approximately every 6-8 feet) around a layout.