☆ Please be sure to read the profile section! This product uses a mechanism where the claws and rail interlock to lock. It allows you to secure the door and open the window for ventilation. I just bought these, but they didn't fit my windows. Both are unused, but I opened the package of one to take out the main unit and test it on my window frame. The other one is unopened. I don't recommend this to those who are concerned about this. I purchased these at a home center for 698 yen (including tax) each. Please note that this product cannot be used unless the gap between the sash (the gap between the outer and inner windows) is 5mm or more. I have uploaded the instructions in the images, so please check them before considering a purchase. Thank you very much. - Brand: nls - Product Name: Kachi Kachi Lock - Function: Security/Ventilation - Installation Method: Easy installation with strong tape - Size Adjustment: Gap adjustment possible (0-80mm)