Abstract: Drive means for a small, lightweight, easily operated syringe infusion pump. A syringe is secured in a holder and the syringe plunger is moved by a pusher block of the drive means. The pusher block is advanced to the syringe plunger by squeezing a finger tab. This simultaneously decouples the pusher block from the internal drive and opens the antisiphon catch to allow quick and easy set-up. The pusher block is moved by the engagement of a floating halfnut on a threaded leadscrew. A force is applied to the halfnut by the block substantially near the midpoint of the leadscrew thereby greatly reducing force mechanisms that attempt to separate the leadscrew and halfnut. A relatively light first biasing means is on the block for applying a relatively small force between the halfnut and the leadscrew.