While being superficially similar to the OM Lupetto, Leoncino, Daino, and Tigrotto, it was an all-new design - except for using the same doors as the earlier "zoological" series (thus called as they were all named after animals).

All but the two lightest models were replaced by the new Z-series in 1976, a design which briefly used OM badging but ended up being marketed exclusively as an Iveco.

Fiat and Unic used the same numerical system followed by NC (for Nafta Cabinato, "diesel cab-over").

[2] Kits for the 35-40 were also sent from Zastava's plant by Iveco for CKD-assembly in Kano, Nigeria, by a company called NTM.

The X-series cab was lightly facelifted a few years after its introduction, when the early metal grille was replaced by a black plastic unit with horizontal bars.