An access device for placing a medical article within a body space, the access device comprising: a dilator having a hub and an elongated dilator body extending from the hub; a guidewire being configured to slide within the elongated dilator body and having a guidewire stop (92A, 92B), the guidewire stop (92A, 92B) being receivable through the elongated dilator body, the guidewire stop (92A, 92B) being shaped to enlarge a cross-sectional dimension of the guidewire relative to adjacent sections of the guidewire; characterized in that the access device further comprises a locking mechanism (30, 130, 230) being removably engaged with and being supported by the dilator prior to the dilator being threaded over the guidewire, the locking mechanism (30, 130, 230) comprising a guidewire lock (44, 144) and a portion having an opening extending therethrough, the opening being of a size and shape configured to receive the guidewire and to inhibit the guidewire stop (92A, 92B) from passing through the opening, the locking mechanism (30, 130, 230) being configured to interlock with the guidewire by interaction between the guidewire lock (44, 144) and the guidewire at least when the dilator is threaded over the guidewire, the guidewire lock (44, 144) having at least one member being moveable between an engaged state and a non-engaged state and being biased toward the engaged state in which the guidewire lock (44, 144) interacts with the guidewire, the locking mechanism (30, 130, 230) and the dilator further being configured to permit removal of the locking mechanism (30, 130, 230) from the dilator by moving the guidewire axially in a proximal direction relative to the dilator with the guidewire stop (92A, 92B) abutting at least part of the portion of the locking mechanism (30, 130, 230) that the opening extends through. a dilator having a hub and an elongated dilator body extending from the hub; a guidewire being configured to slide within the elongated dilator body and having a guidewire stop (92A, 92B), the guidewire stop (92A, 92B) being receivable through the elongated dilator body, the guidewire stop (92A, 92B) being shaped to enlarge a cross-sectional dimension of the guidewire relative to adjacent sections of the guidewire; characterized in that the access device further comprises a locking mechanism (30, 130, 230) being removably engaged with and being supported by the dilator prior to the dilator being threaded over the guidewire, the locking mechanism (30, 130, 230) comprising a guidewire lock (44, 144) and a portion having an opening extending therethrough, the opening being of a size and shape configured to receive the guidewire and to inhibit the guidewire stop (92A, 92B) from passing through the opening, the locking mechanism (30, 130, 230) being configured to interlock with the guidewire by interaction between the guidewire lock (44, 144) and the guidewire at least when the dilator is threaded over the guidewire, the guidewire lock (44, 144) having at least one member being moveable between an engaged state and a non-engaged state and being biased toward the engaged state in which the guidewire lock (44, 144) interacts with the guidewire, the locking mechanism (30, 130, 230) and the dilator further being configured to permit removal of the locking mechanism (30, 130, 230) from the dilator by moving the guidewire axially in a proximal direction relative to the dilator with the guidewire stop (92A, 92B) abutting at least part of the portion of the locking mechanism (30, 130, 230) that the opening extends through.