A medical device for placing an embolic device at a predetermined site within a vessel of the body including a delivery catheter and a flexible pusher member having a lumen therethrough and being slidably disposed within the lumen of the catheter. An embolic device is retained within the delivery catheter by a mechanical interlocking mechanism which includes an engagement member which is attached to the distal end of the pusher member and extends through a retaining ring at the proximal end of the embolic device. A detachment member extends through an aperture at the distal end of the engagement member thereby locking the embolic device onto the pusher member. When the embolic device is advanced to the predetermined site within the vessel, the detachment member is withdrawn from the aperture to thereby release the embolic device at the treatment site.