All Series 1 Fi Collars are rigorously tested for 100 lbs of static pull force in our manufacturing facility, and constructed from fiber-reinforced nylon, Fi Series 2 is reinforced with an internal end-to-end metal frame and tested for 300 lbs static pull force limit.
For dogs with specific behavioral issues, or pullers we recommend using a harness in complement to the Fi Collar for tracking. Depending on the impact speed of a shock load (like a squirrel sighting) the energy delivered to the hinge can exceed a 300 lbs static pull.
For maximum security, ensure the end links on your dog's Fi collar always remain as flat as possible- this means ensuring appropriate size and fit of your dog's Fi collar so there is not enough slack to allow for excessive rotation or movement of the module itself. See Sizing and Fit for further instructions to ensure appropriate size and fit.
For Series 3