Numnuts Logo

Numnuts is a new product under development by 4c Design, in partnership with Moredun Research Institute, for improving the welfare of lambs undergoing necessary but painful animal husbandry procedures.

You can find out more about the overall Numnuts development story here.

Numnuts Tool

Injector Mechanism

The Business Need/Requirements

Field trials had shown that for optimum effectiveness of anaesthesia, the precise location and orientation of the needle tip, prior to delivery of the anaesthetic, was crucial. This meant that a two-stage injector mechanism was required, with the first stage positioning the needle tip, and the second delivering the anaesthetic.

The Project

Working in close conjunction with our colleagues at 4c Design, we investigated several different types of two-stage mechanism, before focusing development on a novel rotary design. This design was then developed through several working prototypes, with new features being added and the size being reduced as the design progressed, always with an eye on space constraints and integration into the Numnuts hand tool. 3D printing techniques were used to great effect to enable rapid iteration through the design process.

Our Activities and Deliverables

  • Over the course of the project, we undertook the following activities:
  • Investigated three different types of two-stage mechanisms: spring clips, breaking knuckles, and cylindrical “clicky pen” mechanism;
  • Designed a novel rotary mechanism, where the second stage of motion would be unlocked once a certain plunger travel had been reached;
  • Re-worked the design to fit into a much shorter space envelope;
  • Gradually added in features such as valves, fluid feed paths, and bottle attachments;
  • Examined options for system breakdown split between tool parts and consumable parts;
  • Designed loading and locking mechanism for consumable;
  • Produced working 3D-printable prototype designs for rapid iteration through development process.


  • Designed and patented rotary two-stage injector mechanism;
  • Prototype injector incorporated into Numnuts hand tool for further field trials;
  • Further development ongoing by 4c Design to miniaturise injector and prepare for mass production;
  • Since 2019, 2000 injectors have delivered 3 million doses of local anaesthetic to happy Australian lambs!