The special fixture is an effective means to realiz precise location and quick installation to work piece.A special clamping mechanism combining with a screw pair and five steel ball pairs is designed and the self-locking feature of the screw pair and the larger force increment feature and higher machinery efficiency of the screw pair is used fully.Its output displacement

force transmission relation and machinery efficiency are studied.The clamping displacement and force on each pair and its machinery efficiency in clamping stroke are shown by an example design.