The paper presents a comparative analysis of the clamping force on the operating parameters of the SB fastening system. An overview of used elastic fastening systems for prestressed concrete sleepers is presented. The results of laboratory research carried out in accordance with the applicable European standards of the PN-EN 13481 and PN-EN 13146 series are described synthetically. Specially prepared clamp type SB with different stiffness within the range allowed by PKP PLK S.A. were selected for the tests. All tests were done in accredited laboratory. The paper presents the impact of the SB clamp stiffness on the basic parameters of the fastening system, such as the clamping force and longitudinal resistance. A reduced value of the static stiffness of the clamp may fail to fulfill the requirements of the fastening system shown in the Technical Specifications for Interoperability. The risk of non-repeatability of the SB clamp should lead to the development of a solution or even a change to the W-type fastening system.