To provide an insert female screw to be threaded to a male screw portion of a knob; pressed into a hole in a plate face in this state while holding the knob in hand, and mounted simply with the half-round rotation of the knob, having improved loosening strength by expanding the insert female screw at its front portion to the outward direction using both the pulling force of the knob on the male screw portion through the half-round rotation and the contact of the knob with a flange face for further more biting it into the peripheral wall of the hole.

Streak protrusions 12d... are formed on the outer periphery wall of a female screw body 12a having a screw groove 12b engraved in the inner periphery face of a resin or metal small cylinder. A plurality of cutouts 12g, 12g are formed ranging from a rear edge 12r of the screw body 12a to the midway in the axial direction for vertically equal-splitting at a corresponding position in the axial direction.