<p>Improved Double Glass Lock - Double glass lock can be applied to heavy doors or windows for added security. And it will be more solid, strong and sturdy, exquisite workmanship, aluminum alloy frame and stainless steel screws can be reused many times. Quantity and Size - Double sliding window lock with 4 glass (approximate volume 6 x 2.54 x 2.4 cm/2.36 x 0.95 x 0.95 inches (L/W/H), suitable for track height greater than 1.2 cm/0.47 inches, thickness of 1.6 cm/0.63 inches (not suitable for mid-way windows) Not suitable for top-way windows, please check your window track before purchasing). Easy to Install - No extra tools are required for installation, each window lock comes with a hexagonal key, which is controlled by the key on the track. Designed for horizontal/vertical windows and sliding glass doors, not suitable for plastic window frames. Widely Used - Can be easily applied to most environments by keeping windows partially open and closed, anti-theft devices and thieves can prevent children from falling and protect the safety of your family while improving air circulation. Product Guarantee and Customer Service - We don't sell picture perfect products, but products that look great if you are not satisfied with our products, we will provide a full refund for free or resend a new product for free. </p>