An apparatus includes a bracket, a pushing member having a pushing surface, a magazine member to fitting about a plurality of clamping rings, a sending member, a fixing member fixed to the bracket and a resisting member fixed to the fixing member. The fixing member defines a positioning hole for fixing the magazine member, with the clamping rings freely sliding through the positioning hole. The sending member includes two guiding rods fixed to the fixing member, two elastic elements fitting about the corresponding guiding rods, and a moving board slidably mounted to the guiding rods. The elasticity of the elastic elements urges the moving board to drive one of the plurality of clamping rings to resist against the resisting member. When the pushing member is moved towards the fixing member, the pushing surface pushes the one clamping ring to clamp a shaft of a connecting piece.