least and , with some going up to . In the past, most infant seats in the US went to and . Infant carriers are often also called "Bucket Seats" as they resemble a bucket with a handle. Some (but not all) seats can be used with the base secured, or with the carrier strapped in alone. Some seats do not have bases. Infant carriers are mounted rear-facing and are designed to "cocoon" against the back of the vehicle seat in the event of a collision, with the impact being absorbed in the outer shell of the restraint. Rear-facing seats are deemed the safest, and in the US children must remain in this position until they are at least 1 year of age and at least . although it is recommended to keep them rear-facing until at least 2 years old or until they outgrow the rear-facing car seat height and weight, whichever is longer. Group 0+ Group 0+ car seats commonly have a chassis permanently fixed into the car by an adult seat belt and can be placed into some form of baby transport using the integral handle if it is the specific model. Rear-facing child seats are inherently safer than forward-facing child seats because they provide more support for the child's head in the event of a sudden deceleration. Although some parents are eager to switch to a forward-facing child seat because it seems more "grown up," various countries and car seat manufacturers recommend that children continue to use a rear-facing child seat for as long as physically possible Position: Sitting, rear-facing, no airbag(with the exception of curtain airbags). Recommended weight: Birth (2–3 kg) to 13 kg (29 lb). Approximate age: Birth to 15 months Convertible seats Convertible seats can be used throughout many stages. Many convertible seats will transition from a rear-facing seat, to a forward-facing seat, and some then can be used as a booster seat. Many convertible seats allow for rear-facing, allowing children to be in the safer rear-facing position up to a weight of . Convertible safety seats can be installed as either rear-facing or forward-facing. There is a large selection available to choose from and weight limits, height limits, and extra features vary from seat to seat and by manufacturer. Seats with a 5-point harness are considered safer than those with an overhead shield. Convertibles aren't considered the best choice for a newborn