When connecting, pressure is required to move the fluid pathway spike through the internal barrier and then through the septum. The resistance you feel is the pressure inside the connector that ensures a tight septum seal and a completely covered internal fluid pathway. A tight, straight connection is needed to completely access the fluid pathway. Otherwise, you might be connected, but the fluid pathway spike has not fully cleared the septum entering the syringe or IV tubing. Use only a luer lock syringe or tubing. Slip tip syringes (such as ABG syringes), slip tip blood collection devices and slip tip tubings will not connect to the Invision-Plus® Needleless IV Connectors.