The rail base width measurement is per NMRA specs of

Smooth rolling blackened metal wheels on all Bi-level cars with all-wheel electrical pickup

Model Number: 94826

Here is a Lionel 6-19806 O Gauge Pennsylvania Operating Hopper from 1988

Layout dimensions: 40 inches x 60 inches

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