Adjustable volume pipette with improved volume adjustment lock mechanism

A volume adjustable pipette for aspirating and dispensing precise volumes of liquid comprising:

• an elongated hollow hand-holdable housing;
• a plunger supported for turning and for axial movement within the housing and including a thumb engageable upper end extending above a top of the housing;
• an upper stop for the plunger axially adjustable within the housing in response to a turning of the plunger to adjust the volume of liquid drawn into a tip secured to a lower end of the housing upon upward axial movement of the plunger to the upper stop;
• a manually actuated lock mechanism for locking the plunger against rotation to set the volume adjustment for the pipette comprising a hand-turnable knob for actuating and releasing the lock mechanism;
• a hollow volume screw axially receiving the plunger for turning with the plunger within and relative to the housing and for axial movement relative to the plunger;
• a gripping member extending from an inside of the housing to engage an outer surface of the volume screw, the gripping member comprising a annular collet engaging an outer surface of the volume screw and including an outer cam surface;
• the hand-turnable knob carrying a cam surface for engaging the annular cam surface of the collet to urge the collet against the volume screw to lock the volume screw relative to the housing upon an annular turning of the hand-turnable knob in a first direction;
• and
• the upper stop being secured within the volume screw to engage a shoulder on the plunger to limit upper axial movement of the plunger within the housing.