## 3 Results  
In order to validate the proposed analytical method, experimental tests were conducted. In particular, a total of six models of FLT and three interchangeable pieces of equipment were selected. The FLTs had a rated capacity of 2 \(\div\) 2.5 tons, a maximum lift height of 3 \(\div\) 5 m, and a load centre of gravity at a horizontal distance of 500 mm from the front face of the fork arm shank. With reference to Figure 7, the selected interchangeable equipment included:  
* The lateral displacement--is used for the lateral displacement of the fork arms of a predetermined length. It has a rated capacity of 2500 kg, a horizontal distance of the load centre of gravity from the fork carrier of 600 mm, a weight of 55 kg, a horizontal distance of the interchangeable equipment centre of gravity from the fork carrier of 37 mm, and a lateral displacement of 100 mm. * The clamp with parallel arms--it is used for handling cardboard bales, wool, garbage, reels of cellulose, foam blocks, concrete blocks, kegs, reels, etc. It allows the clamp to load by means of the parallel motion of its forks/arms. It has a rated capacity of 1900 kg, a horizontal distance of the load centre of gravity from the fork carrier of 637 mm, a weight of 448 kg, a horizontal distance of the interchangeable equipment centre of gravity from the fork carrier of 249 mm, and a lateral displacement of 313 mm. * The clamp for reels--it is used for handling paper reels of a different nature. This attachment can also continuously rotate the load. It has a rated capacity of 2000 kg, a horizontal distance of the load centre of gravity from the fork carrier of 852 mm, a weight of 620 kg, a horizontal distance of the interchangeable equipment centre of gravity from the fork carrier of 235 mm, and a lateral displacement of 425 mm. For each combination of the aforementioned FLTs and interchangeable equipment, the rated capacity of the assembly (FLT + interchangeable equipment) was evaluated by means  
Figure 6: Analytical assessment of assembly-rated capacity. Figure 7: Interchangeable equipment: (**a**) Lateral displacement, (**b**) Clamp with parallel arms, and (**c**) Clamp for reels. aforementioned factors that affect the stability of a FLT. Standard ISO 22915-2 defines the stability tests that need to be performed. With reference to the aforementioned standard, in [8], the stability equations were derived with detailed derivations for the four kinds of stability tests. The effects of acceleration and centrifugal forces were also additionally included in the equations. However, according to the authors' knowledge, at present, the analytical procedures that are at one's disposal refer to FLTs with forks. No analytical procedures are available to evaluate the stability of FLT when combined with interchangeable equipment. A useful guide for identifying interchangeable equipment can be found in [24], where the European materials handling federation (FEM) proposes a classification for the attachments of the FLT with reference to the applicable legislation and on the basis of the documentation available to date and the technical knowledge of its members (industrial trucks manufacturers and attachment manufacturers). Hence, the analytical method herein proposed is focused on filling this gap. It is mainly based on the static equilibrium (force and moment) of a rigid body. Even if this simplified approach is not able to mimic the flexibility of the FLT structure and the dynamic effects of the lifting operations, it is able to capture the changes introduced by the interchangeable equipment in the rated capacity of the FLT with forks. The proposed analytical approach takes into account both the fact that FLT has to fulfill stability requirements defined in ISO 22915-2 and that the actual capacity at a maximum lift height with the load centre distance should accordingly be provided by the FLT's manufacturer.