The Britax Infant Positioning Insert may be necessary for small infants to achieve a snug fit of the harness around you child. The Infant Positioning Insert has been tested and certified for use with the following BRITAX convertible car seats: ROUNDABOUT 55, MARATHON 70, BOULEVARD 70, BOULEVARD 70 CS, and ADVOCATE 70 CS. Britax has been a pioneer in child passenger safety for more than 35 years, with a legacy of leadership in developing innovations that enhance the safety of child car seats and improve their ease of installation and use. Their uncompromising focus has made Britax the best-selling child seat in Europe and one of the brands most trusted by American parents and caregivers since entering the U.S. market in 1996. Their commitment to improving child safety is unparalleled, as evidenced by the fact that all Britax products undergo the most rigorous testing in the industry at five Britax testing facilities worldwide. They work closely with vehicle manufacturers to encourage design improvements that enhance the performance of child car seats. In addition, they maintain an ongoing dialogue with consumers, child passenger safety technicians and other child safety advocates to ensure proper installation and use of child car seats and develop new ideas to improve their safety and ease of use.