A modular prosthesis kit includes a sleeve. The sleeve has a central portion and a fin. At least part of the central portion includes a plurality of adjacent terraces. The fin includes a pair of tapered outer surfaces that are continuous, non-terraced and define a wedge-shape to stabilize the position of the sleeve when implanted. The sleeve may include a single terraced spout or wing with such a fin or may not have any spouts or wings extending out from the central portion. The kit may also include sleeves with two spouts or wings extending out from the central portion.