This hold-back is a white glass knob with black and white harlequin check pattern.  It measures approx 1 1/2" in diameter. The image on the right shows the piece which goes on the front of the curtains, and the image to the left shows the back piece, which has the magnet mounted on a coordinating  plastic piece.  Note that these will not work on heavy lined drapes, but do well on sheers or lightweight curtains.  The price is for one pair.