Hongye Double Rhomb Handwind 17 Jewels

A very easy to adjust clasp and also found on many inexpensive watches
This type of clasp is still very popular in Asia and can be found from India's hmt watches to Casio's lower tier models. And this mechanism is in fact pretty ingenious. The left part can be lift up with a ball pen or a paper clip and then adjusted for the size of the wrist. While it is a very simple and inexpensive clasp, I still admire the design. No need to use tools to take out links from the bracelet and adjustable without any tools.