The rail base width measurement is per NMRA specs of

Offset twin hopper kit

Here is an Athearn 16722 HO Scale Union Pacific SD40-2 Diesel Locomotive w/DCC & Sound #1618

and Kato magnetic knuckle couplers

The Trainz SKU for this item is P11570075

Roco 476 1:87 Minitanks Fla Rak PZ Roland VariantsUnitPrice_number_38.40 The rail base width measurementThis is a Roco 476 1: 87 Fla Rak PZ Roland Condition: Factory New (C 9) Operational Status: Functional Original Box: Yes (P 9) Manufacturer: Roco Model Number: 476 MSRP: $19. 99 Scale Era: HO Scale Model Type: Vehicles The Trainz SKU for this item is P12504301. Trainz Product Id: 12504301