Size it from the screw out.
Type what you measured on each side of the door, from the centre of the fixing screw to the outer face of the handle. The barrel redraws to scale, so what you see is what turns up.
Drag to turn the barrel
Type what you measured on each side of the door, from the centre of the fixing screw to the outer face of the handle. The barrel redraws to scale, so what you see is what turns up.
Drag to turn the barrel
Keep scrolling. The barrel turns, opens up to show the pins and springs either side of the cam, then puts itself back together.