Trainz/Overview of Attachment Points
Attachment points are created in the 3D modelling software used to create an asset. Their purpose is to specify the exact coordinates where one asset item/sub-mesh/effect connects to another, for example, where the track connects onto a bridge, or where the cab is placed inside a locomotive. All attachment points are referenced in the config.txt file of an asset to define its use and function.
Attachment points must follow strict naming conventions provided in the Content Creation Guide for their implementation in Trainz. In 3DS Max and Gmax, attachment points should always be placed in top view with for the orientation of the axis to be correct. They may then be rotated if needed. If creating a Locomotive, the train should be facing down the page in top view.
Commonly Used Attachment Points on Locomotives 
a.limfront: front of train
a.limback: rear of train
a.bog0: front bogey
a.bog1: back bogey
a.bogx: any other bogey
a.cabfront: front cab
a.cabback: rear cab
a.outsideviewx: external cameras
a.whistle: whistle/horn particle effect
a.sitpointx: sitting passenger
a.standpointx: standing passenger