I was ready to jump on this post, but I decided that 50cc was having a translation problem and did not want to confuse things.
After reading Fred's post, I think you should tell the guy at 50cc what the correct terms are from Fred's post. Give him the English name too (it is correct, the English worry a lot about keeping thier gudgeons under conrol.
Now, back to your problem. Someone posted a while ago with a similar problem. He had allready received a kit with the wrong size wrist pin and had to have a replacement shipped. I am sure this is why they are now asking the question.
If you search the last 3 months or so with piston, pin, bushing and whatever else you can think of, you should find the thread.
My recolection is that the supplied wrist pin was too small and someone else posted something about the US model having a larger wrist pin and he made adaptor bushings. I may have this backward.
If you can't find the thread, or it is inconclusive, pull the cylinder and measure the diameter of the wrist pin. It is the hollow pin that attaches the piston to the connecting rod and allows the oiston to rock, like a hand on a wrist.