Here is a picture of the locking mechanism:
One or the rarer versions of the Kakola handcuffs went up for auction in 2008. It went for $5,432! (Not that your set would go for that much. There are many factors that determine the price.)
Images thoughtfully provided by Lars Holst who has one of the world's rarest (and coolest) handcuff collections. See his site at The Lars Holst Restraint Collection for more handcuff and other restraint photos.
Feel free to email me if you have and Kakola handcuff photos that you would like to share!