This creation is a kind of syringe (two), comprising: a syringe, an adapter and a push rod. The interior forward end of syringe is equipped with an annular stop portion, and annular blocking part has at least two limited blocks and at least two limit clip ditches, and limit clip ditch is obstructed by limited block to be formed, and one of limited block side-line forms a guiding face. The adapter installs the what syringe interior forward end, at least two clip locating pieces are equipped with around the adapter, one of each clip locating piece side-line is equipped with a guiding incline, when adapter installs what syringe interior forward end, by the contact of guiding face and guiding incline, clip locating piece can be guided and limited block makees positioning and block, use the rotation for limiting the adapter, adapter is effectively positioned into what syringe interior forward end, uses avoiding that there is a situation where adapters to fall off.本創作係一種注射器(二)，包括：一針筒、一轉接頭及一推桿。針筒的內部前端設有一環形限位部，環形卡掣部具有至少二限位擋塊及至少二限位卡掣溝，限位卡掣溝由限位擋塊所阻隔形成，限位擋塊之一側係形成一導引面。該轉接頭裝設於該針筒內部前端，該轉接頭的周圍設有至少二卡掣定位件，每一卡掣定位件之一側係設有一導斜面，當轉接頭裝設於針筒內部前端時，藉由導引面及導斜面的接觸，可以導引卡掣定位件及限位擋塊作定位與擋止，藉以限定該轉接頭的轉動，有效將轉接頭定位於針筒內部前端，藉以避免發生轉接頭脫落的情況。
