Easy to install: There is no need to install extra tools,it equips a hex key in each window locks,holding on the track by key control. Durable material: It is strong,solid and sturdy,exquisite workmanship,aluminum alloy frame and stainless steel screws that can be took full advantage of many times. Wide usage: It can be easily applied to most environments.By keeping the windows partially open and closed, the burglar-proof and thieves can prevent children from falling and protect the safety of their families while improving air circulation. Specifications: Size: 3 x 2.4 x 2.4 cm/ 1.18 x 0.94 x 0.94 inch(LWH) Material: aluminum alloy and stainless steel Quantity: 4 pieces Package includes: 4 x Sliding window locks with keys