HOn3 Standards Gauge
... Designed and developed by the NMRA (National Model Railroad Association) Engineering committee, this pocket sized gauge enables you to check all important dimensions on your track and rolling stock as follows: * Gauge of track and turnouts * Flangeway depth and "check gauge" * Clearance * Height of loading platform
If cars do not run correctly, this gauge will help you pinpoint the trouble. Complete instructions come with each gauge.