We recently had a discussion on wheels, and why the
outside of the wheel rim is often shiny. One reason
given was self guarded frogs.

I just found another! On page 42 of Four Way's West
"California Rails" there is an explanation of a device
called a "house top". This sits outside the rail at the
points of the switch, and pushes the flange of a wheel
AWAY from the point to reduce wear on the point rail.
The author notes this device can only be used on low
speed track, like in a yard. The example comes from the
SP's Guadalupe, California yard.

This detail can actually be modeled on practically any
layout, since it doesn't actually have to work.

Tim O'Connor