An oral care implement handle or a refill head therefor. The refill head may include a sleeve portion extending from a proximal end to a distal end, the sleeve portion having an inner surface that defines an internal cavity. The internal cavity may extend along a sleeve axis from an open bottom end at the proximal end of the sleeve portion to a closed top end, the internal cavity being configured to receive an attachment portion of a stem of an oral care implement handle. The internal cavity may have a proximal section adjacent the open bottom end and a distal section adjacent the closed top end. The distal section of the internal cavity may include a central portion located on the sleeve axis and at least one slot portion radially extending from the central portion.