Fletcher Terry Picture Perfect Frame Hanging System 2 Frame Blister Pack
Features two keyhole steel bridges screwed to either side of the back of the frame. The really clever bits are the fixing buttons, with marker points.
First, put buttons into the bridges and tape the little spirit level onto the top of the frame. Offer the frame up to the wall, get it level and press buttons firmly to the wall. The points will mark the wall. Remove buttons from bridges and pin them to the wall, in the marked positions. Place the frame over the buttons and push down. For best results fit felt bumpers to the bottom of the frame.