There is 2-3% difference according to manual measurement.

Feature:
  The way it works is, you simply place it on the top corners of your window frame and tap it in with a hammer.
    It'll make two tiny holes the size of a thumb-tack, and by using the leverage of a bar that goes alongside the edge of the frame, it safely hold the curtain bar up with ease.
    The curtain rod holders are able to hold up to 20 lbs of weight without damaging your walls, and won't require you to level or adjust anything after installation as it'll always be as level as your window frame.
    The Hang curtain rod holders work with any wooden window frame that's at least 1/2 inch wide from the wall, will fit any curtain rod up to 1 inch in diameter, and there's even an option for a center support bracket for extra long windows and curtains.
    The unique easy hanging curtain rod holders require just a hammer or mallet as they require not drilling or nails, are easily removed with no damage left afterwards, and they come in single or double rod holders depending on your preference.
    The double rod holder protrudes 4.25 inches from the wall.
    Material: A3 iron plate
    Size:as shown
Package includes:
    2 X Single/Double Center Curtain Rod Bracket (Depends on your choice)