The use of the product: Used for the connection of sofa backrest and seat back, can adjust the height of the sofa backrest, so that it can be converted from a sofa to a bed, suitable for connecting armrests and seats, backrests and seats, pillows and backrests, armrests and backrests, bed frames and beds, etc. Through the operation of the gears, change the angle adjustment between the armrests, backrests, pillows, seats and the beds, the installation is hidden and safe, the use of gears to open and close the card position design, multi-angle, multi-position gears. Features: 1. Superb storage function, a comprehensive solution to your lack of space problem 2. Sofa bed spring lifter first-class cold-rolled steel strong spring, can be multi-angle, multi-position adjustment of the sofa bed or cabinet box 3. Large capacity storage space at the base: quilts, pillows, books, musical instruments can all be organized Sofa bed hinge