Fork arm extensions are intended to be fully engaged with the load, i.e. the load should be against the fork shank. Fork arm extensions are not designed to be tip loaded, and at least 50% of the load should always be supported by the parent fork arm.
Fork arm extensions intended for fork arm blade lengths ≥ 750 mm manufactured in accordance with ISO 13284 allow an overhang (increase in length) of 66.7%, i.e. at least 60% of the fork extension shall be supported by the parent fork arm.
For example, fork arms 1200 mm long can be increased by a maximum of 800 mm, to 2000 mm, using ISO 13284 fork extensions.
Fork arm extensions manufactured in accordance with ANSI B.56.1 allow an overhang (increase in length) of 50%, i.e. at least 66.7% of the fork extension shall be supported by the parent fork arm.
For example, fork arms 1200 mm long can be increased by a maximum of 600 mm, to 1800 mm, using ANSI B.56.1 fork extensions.
In all cases, the fork arm extension should be marked with the blade cross section and minimum length of the parent fork arm that it can be used with. Where the load centre distance with the fork extension fitted exceeds that shown on the truck capacity plate the truck shall be de-rated accordingly. Both the rated capacity of the truck and that of the fork extension shall be respected.