32 is clear of the valve member 22 when the hub is inserted fully into the cavity in use for example in an intravenous drip procedure a conventional air pervious blanking hub 34 is inserted into the needle hub 32 cavity as shown in fig9 the needle 30 and cannula 28 are then located in the patient 39 s vein the transparent hub 34 as is conventional serves as an indicator that the needle 30 is correctly located when it becomes blood filled the person carrying out the procedure then presses down with a finger on the rear portion of the bulge zone 20 and withdraws the needle 30 together with the plug 34 from the patient as the sharpened tip of the needle passes the valve member 22 which is pressed down on the needle 30 as it is withdrawn from the body 10 the bulge zone is pressed downwardly into the cavity 16 of the body 10 the bulge zone 20 obviously has a greater area than its more rigid surround the dotted line in fig3 and this larger area together with the fairly stiff resilience of the plastic material from which it is made causes the material of the bulge zone to snap into the body with an over centre action as it is pressed inwardly beyond the dotted line position in fig3 when the bulge zone 20.