Single rope grab Work Principles: Close: When the grab need to close, just put the opened grab on the materials, the put down the crane hook till the grab slide seat is put on the grab gallows, then lift the crane hook, the gallows rise with the slid seat , the grab close. Open: When the grab need to open, put the filled grab on the ground or the material, then lift the crane hook, the slide seat rise with the hook, in this time, the gallows have slipped out from the slide seat automatically, the grab open and unload the cargo. NOTE:please show these informaions in your inquire : one : how much is your crane total lifting capacity ? which material the grab will unload ? or two :if you have ensure the grab volume,then tell me which material the grab will unload ? we can provide a perfect proposal for you with the informations you give to us .