of the opening 64 the bending moment imposed on the needle by the misalignment of the normal i e unstressed longitudinal axis of the needle with the longitudinal axes of the carrier and housing causes the needle to curve concave upwardly as shown in fig9 as the carrier and needle move farther to the right to the fully retracted or second position the left end of the needle clears the opening 64 and snaps up to the position shown in fig1 so that the needle is no longer in alignment with the opening 64 and cannot be moved either accidentally or deliberately back to the exposed position as with the tab of the embodiment shown in fig1 6 the tab on the carrier shown in fig7 9 is designed so that it can easily be snapped off as shown in fig1 by the use of only one hand fig1 and 12 show another embodiment of the invention in which a carrier 80 in a housing 81 includes an elongated right cylindrical body 82 with a frustoconical head 84 formed integrally with the left as viewed in fig1 and 12 end of the body the head tapers outwardly toward the left the maximum diameter of the head is greater.