An apparatus is provided for automatically mounting a helix on a radial bristle cosmetic brush, and in particular, a mascara brush. The brush has a twisted wire core and may be mounted to a plastic stem or rod that extends back to a cap/handle combination. The helix comprises a spiral series of adjacent coils. The helix is adapted to be mounted about the core of the brush such that the radially extending bristles of the brush project out between adjacent coils of the helix. The apparatus for mounting the helix on the brush comprises a base supporting a cradle. The cradle receives and aligns a helix and a brush. A pusher mounted next to the cradle slides the brush toward the helix such that the tip of the brush comes to rest against one end of the helix. A gripper holds the other end of the helix so that the helix is stationary relative to rotation of the brush. A rotator has a pair of jaws supporting wheels that grasp the stem of the brush. At least one of the wheels is driven to rotate the brush. As the brush is rotated, the helix is 'threaded' onto the brush in much the same way as a nut is threaded onto a screw. The gripper is mounted on a carriage that permits it to move freely toward the brush as the helix is drawn onto the brush. After the helix is drawn onto the brush, the rotator and gripper release the brush and helix assembly.