Tolerancing is a key step in the product life cycle and aims at improving the product quality and its assemblability as well as reducing the overall costs and time to market. Especially, the tolerance allocation and transfer are two important engineering functions involving a direct impact on compliance with functional and manufacturing requirements. However, on the one hand the traditional approaches reduce the tolerance values during the transfer of design dimension on manufacturing dimensions, and on the other hand neglect the difficulty of manufacturing dimension obtaining. Thus, this paper proposes an unique transfer approach of mechanism-dimension allowing the transposition of the functional requirement into part manufacturing dimensions. In addition, this work uses an innovative tolerance allocation method considering the difficulty of obtaining manufacturing dimensions. This difficulty is evaluated through a mathematical coefficient calculated using the Failure Mode, Effects and Criticality Analysis (FMECA) tool. The failure causes are the different sources of the manufacturing difficult. The obtained results lead to avoid tolerance reduction generated by the double dimensions transfer of traditional industrial approaches. Moreover, the manufacturing dimension tolerances, which are difficult to obtain, are widen. Therefore, the total costs, considering manufacturing cost and quality loss, decreases. The main contributions of the proposed model are shown through a case study.