Trundle Arms Applications Tubular Trundle Arms are for mounting the Top Spring unit. They are also an ideal replacement for the old day bed. You can take the daybed spring off and use these Tubular Trundle Arms for better strength and stability or a completely new look. What Is Included The Trundle Arms are packed in pairs and include the necessary hardware for attachment. Fit Any Daybed The 39" Trundle Arms fit any daybed end and keep the rails at a standard height of about 15 1/4" off the floor.