The paper summarizes the research of the iNEMI (International Manufacturing Initiatives) project on Fiber Connector Endface Specifications focused on the development of the cleanliness specification of the receptacle modules. It will discuss (1) the critical parameters of Small Form-Factor (SFF&SFP) modules sensitive to the contamination, (2) the experimental contamination techniques, (3) the test and measurement methodology, as well as (4) the Gage R & R (Repeatability & Reproducibility) studies. We choose one of the standard OC-48, SFF modules manufactured by Sumitomo Electric as the experimental vehicle for the project. The influence of the SiO2 based dust with the particle size under 149 um on optical performance of SFF module has been investigated. The Optical Return Loss (ORL) has been identified as the most sensitive parameter to the contamination for the both transmitter and receiver optical endface. In a case of changes of the transmitter ORL by 20-25 dB due to the application of the contamination, the optical power and spectral width didn't change, and the pulse mask was reduced only by 2%. The contamination near the core area caused changes of the ORL by 20-30dB, and high standard deviation of ORL (0.5-2.1 dB). The Gage R & R study was focused on investigation of equipment repeatability, mating repeatability, and operator dependence for ORL measurement of clean and contaminated optical endface. The proposed experimental methodology was able to achieve all Gage R & R parameters within the required limits.