US Patent 7214208 Needle guard

The needle guard employs a spring clip that has a pair of apertured locks through which the needle passes. The aperture in the foremost lock is defined by cutouts that deflect inwardly upon withdrawal of the needle in order to block a return passage of the needle. The end of the needle is enlarged to abut against the rearmost lock and to further prevent a return passage through the foremost lock. The enlarged end of the needle is trapped between the two locks after being drawn into the needle guard.