An access device for placing a medical article within a body space, the access device comprising: a guidewire having a guidewire stop (92A, 92B), the guidewire stop (92A, 92B) being shaped to enlarge a cross-sectional dimension of the guidewire relative to adjacent sections of the guidewire; a dilator configured to be coaxially disposed about the guidewire; characterized in that the access device further comprises a locking mechanism (30, 130, 230, 330) being removably engaged with and disposed on the dilator prior to the dilator being coaxially disposed about the guidewire, the locking mechanism (30, 130, 230, 330) comprising a portion having an 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, 330) being configured to move from an unlocked state to a locked state, the locking mechanism (30, 130, 230, 330) being disengaged from the guidewire when the locking mechanism (30, 130, 230, 330) is in the unlocked state so as to allow axial movement by the guidewire through the locking mechanism (30, 130, 230, 330) in a proximal direction and a distal direction relative to the dilator, the locking mechanism (30, 130, 230, 330) being engaged with the guidewire when the locking mechanism (30, 130, 230, 330) is in the locked state so as to limit at least axial movement of a portion of the guidewire in the distal direction relative to at least a portion of the dilator, the locking mechanism (30, 130, 230, 330) and the dilator further being configured to permit removal of the locking mechanism (30, 130, 230, 330) 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, 330) that the opening extends through. a guidewire having a guidewire stop (92A, 92B), the guidewire stop (92A, 92B) being shaped to enlarge a cross-sectional dimension of the guidewire relative to adjacent sections of the guidewire; a dilator configured to be coaxially disposed about the guidewire; characterized in that the access device further comprises a locking mechanism (30, 130, 230, 330) being removably engaged with and disposed on the dilator prior to the dilator being coaxially disposed about the guidewire, the locking mechanism (30, 130, 230, 330) comprising a portion having an 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, 330) being configured to move from an unlocked state to a locked state, the locking mechanism (30, 130, 230, 330) being disengaged from the guidewire when the locking mechanism (30, 130, 230, 330) is in the unlocked state so as to allow axial movement by the guidewire through the locking mechanism (30, 130, 230, 330) in a proximal direction and a distal direction relative to the dilator, the locking mechanism (30, 130, 230, 330) being engaged with the guidewire when the locking mechanism (30, 130, 230, 330) is in the locked state so as to limit at least axial movement of a portion of the guidewire in the distal direction relative to at least a portion of the dilator, the locking mechanism (30, 130, 230, 330) and the dilator further being configured to permit removal of the locking mechanism (30, 130, 230, 330) 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, 330) that the opening extends through.