The Wheel Gauge checkes the back to back measurements of model railway wheels. Getting the right dimension ensures the rolling stock travels through points and crossing without derailing or generating excessive movement and noise. Our gauge is set to 14.4mm - the correct width for standard OO gauge track. It~s ideal for all Hornby, Bachmann and Dapol etc items. The gauge should be a friction fit - if not adjust the wheels on the axles or replace as necessary.