iPhone - What is the size of UIslider's thumb?

I am using the UISlider's set开发者_JAVA百科ThumbImage:forState to customize the look of slider's thumb. But this looks much bigger. The image that I'm using is of size 55x55 pixels. What should be the size of image that i've to use?

From XIB, i found that, the height of UISlider is 23 pixels. And when I changed the image size to 23x23 pixels, it looks perfect now.