A replacement head for detachable coupling to an oral care implement body. The replacement head may include a head having at least one treatment element and a tubular sleeve extending from the head and defining a cavity having an axis that receives a stem of the oral care implement body. The tubular sleeve may have a proximal edge that defines an opening into the cavity. A slot in the tubular sleeve is configured to mate with a boss of the stem of the oral care implement body. The slot may include an entry slot section extending from the proximal edge of the tubular sleeve towards the head and a locking slot section extending from the entry slot section towards the head. The locking slot section may have a first lateral wall that is oblique to the cavity axis and a second lateral wall that is parallel to the cavity axis.