I'm selling because I only used one out of the four that I purchased! This product was great for childproofing door locks. Originally, this product costs around 3,700 yen for a set of four. It's a very sturdy product. Product Details 【Material】: High-quality aluminum alloy, durable and scratch-resistant 【Anti-theft measures】: Auxiliary lock for window glass and aluminum frames. Prevents mischief by children and pets, and prevents crime. 【Ventilation】: You can lock the window frame while it's slightly open, which is convenient for ventilation in bathrooms, kitchens, toilets, etc. 【Lightweight design】: It twists to lock, making it convenient and fast, and you don't need to use other keys, making it difficult for children to open 【How to use】: Insert the window lock into the groove and turn the knob to secure it firmly.