What's the difference between a butt ramp and a curb ramp?
A butt ramp doesn't have a bevel at the top which would normally lie on the threshold. Instead, it butts up to the threshold. It has legs underneath and will be used when a door swings out.
A curb ramp is used when a door swings in. This has a bevel on both ends and will lie on the threshold.
What's the difference between a bevel and a threshold ramp?
A bevel is at the bottom of a ramp which aids in a smoother transition from the ground to the ramp, or the ramp to the ground.
A threshold ramp is typically used for 1-2" elevations. It is used for a smoother transition from outside on the ramp to inside your home.