63 is formed of plastic material and is clung to threadedly secure to the outer end 61 the provision of enlargement 63 may facilitate user to push or pull connection member 60 further a plurality of hooks 32 a and 32 b are provided on inner wall 31 of inner member 30 furthermore the same number of tabs e g 64 a and 64 b are provided on a side of connection member 60 tabs 64 a and 64 b are received in hooks 32 a and 32 b for mounting connection member 60 on inner member 30 thus connection member 60 may slide on inner wall 31 of inner member 30 back and forth then fixedly attach both ends of elastic member 80 to inner member 30 and connection member 60 respectively for ensuring a sliding secure relationship between connection member 60 and inner member 30 in the embodiment elastic member 80 is formed of flexible metal wire and has one end affixed to inner member 30 and the other end affixed to connection member 60 a slide travel limitation mechanism is provided as shown an elongate opening 34 is provided near the outer end of inner member 30 and a locking pin 65 is provided on connection member 60 locking pin 65 is slidably received in opening 34 as such a uniform elastic force provided by elastic member 80 is exerted on connection member 60 when outer member 20 is pulled outwardly also connection member 60 is prevented from further moving when outer member 30 has reached the use position because the confinement of locking pin 65 in opening 34 this can avoid any potential irregularity a front cam 66.