Sleeve anchors come in different styles such as: Acorn nut style, Flat head style and Hex nut styles.
Sleeve anchors work by expanding against the material in which it is embedded. When the head is turned clockwise, the conical end is pulled into the sleeve, pushing it outward 360 deg around the anchor into the masonry.
They are designed to be used in solid or hollow masonry, including cinder block, brick, marble and concrete. One advantage of sleeve anchors is that it can be removed after it's been installed. Another is that the length of the sleeve induces less stress on the substrate than does a wedge anchor. The sleeve anchor is preferred when a decorative finish look is desired.