Variable pipette

A variable pipette comprising:

• a substantially tubular body (1) having means defining a first opening at one end thereof, means defining a second opening at the other end thereof, and a positioning portion (1a) provided at a predetermined position on an inner periphery of the body;
• a substantially tubular cylinder (3) rigidly secured to the first opening of said body;
• a nut (7) having an inner peripheral threaded portion (7a), a first first-stage stop portion (7b), and a first second-stage stop portion (7c), said nut (7) being inserted in said body between said positioning portion (1a) and said cylinder (3) such that said nut is unable to rotate relative to said body but is axially slidable relative to said body;
• a second-stage spring (31) accommodated within said body and arranged to bias said nut rearwardly so that said nut is brought into contact with said portion (1a);
• a threaded hollow shaft (9) inserted into the second opening of said body, said shaft (9) having a first step portion (12b) at a rear portion thereof and an outer peripheral threaded portion (9c) at a forward position thereof, said outer peripheral threaded portion being in threaded engagement with the inner peripheral threaded portion (7a) of said nut so that said shaft is rotatable;
• an actuating shaft (25) received in said hollow shaft (9) in such a manner that said actuating shaft is rotatable together with said hollow shaft as one unit and is axially slidable relative to said hollow shaft, said actuating shaft (25) having a second first-stage stop portion (29a) at a forward portion thereof which projects from the forward portion of said hollow shaft, said second first-stage stop portion (29a) facing the first first-stage stop portion (7b) of said nut across a space which defines a first-stage stroke (l.sub.1), said actuating shaft further having a second stop portion (25d) and an actuating portion (26) at a rear portion thereof;
• a plunger (27) received in said cylinder to define an airtight cylinder chamber (3a) within said cylinder, said plunger being movable at least axially together with said actuating shaft (25) as one unit;
• a first-stage spring (30) accommodated within said body (1) and/or said cylinder (3) such as to bias said plunger (27) and said actuating shaft (25) rearwardly thereby bringing the second stop portion (25d) of said actuating shaft into contact with said first stop portion (12b);
• and
• a second second-stage stop portion (2a) provided on either said body or said cylinder so as to face the first second-stage stop portion (7c) of said nut across a space which defines a second-stage stroke (l.sub.2).