Abstract: An anchor assembly for installing a threaded roof bolt under tension in a bore hole formed in underground passageways, mines, and the like. The anchor assembly includes a conventional two compartment resin cartridge and a mechanical expansion unit. A support collar is threaded on the bolt to restrict axial movement of the mechanical expansion unit. The mechanical expansion unit includes a camming plug and an expandable shell. A pair of hollow tubular sleeves are positioned intermediate the camming plug and the support collar to prevent the resin from embedding in the grooves of the threads of the bolt. Accordingly, the bolt is free to rotate relative to the substrate.