SM_CXDRAG top-level constant
The number of pixels on either side of a mouse-down point that the mouse pointer can move before a drag operation begins. This allows the user to click and release the mouse button easily without unintentionally starting a drag operation. If this value is negative, it is subtracted from the left of the mouse-down point and added to the right of it.
const SM_CXDRAG = 68;