Questions about Samsung Sport Band

According to our information, it has a length of 86,4 mm and is 26,8 mm wide.

According to the product specifications yes :)

20mm as it says in the description. There is an 'M' stamped on the arbmand.

yes, these are the official replacement bands from Samsung.

Unfortunately, I can't say that because I bought this bracelet for my Galaxy Watch2.

I would say it is S/M, in these colors, there is usually no M/L (since "female colors")

20 mm, there are no other indications for this product. Sorry.

According to research, the bracelet has a length of approx. 20.5 cm.

Yes.