Offset forks are designed primarily for the purpose of enabling the forks on the lift truck to be wider than the carriage (fork carrier). It is important to note that by doing this the load capacity of the fork will need to be re-evaluated. Inset forks, which make the forks narrower than the carriage, can also be designed. Inset forks are usually required to fit around a vertical centre support bar on the carriage. Consideration should be given to the load now being carried on the extreme edges of the forks. This can impose some twisting and some additional load on the edges of the hooks. 
When offset, the blades of the left and right hand extend further out than the upright portion of the fork. Custom specifications will dictate what the required dimensions will be. The opposite will apply to inset forks.