During my childhood I was spanked something like this:
~ 40% - with the belt;
~ 40% - with the switch;
~ 20% - with a wooden ruler or a wooden spatula from the kitchen
For me, the most painful was the switch. Applied with full force, it really blistered my butt. The blistered stripes persisted around 2, 3 or even 4 days after the spanking was over.
A few hours after, the stinging was really painful, the first night was like a nightmare trying to sleep on my tummy and the next day I was still have problems trying to sit...