Is it critical to get the dimensions absolutely correct?
Because if you don’t mind that it’s slightly off, that photo is good enough to measure in and work out a good approximation of the real size if you have dimensions of the plate it’s mounted on.
Using the measuring tool in Photoshop, the height of the bracket is 48 pixels while the height of plate (at the left edge of the bracket) is 237 pixels. Similarly, the width of the bracket is 91.6 pixels and the plate width is 267.5. The depth of the clip seems to be about the same as the width of the plate alongside it.
If you measure up the real plate where the white and blue arrows are (that’s especially important for the white one), you can work out the approximate size of the clip easily enough.