This indicates the minimum tensile strength of the elastomer. If the designation has an M after the Revision Year, then this callout is stated in Metric units, megapascals (MPa). If no M is present, then the callout is specifying the English unit, pounds-per-square inch (psi). In this example, the 14 is calling-out 14 MPa. The conversion to psi is: MPa x 145 = psi. Therefore, the psi Tensile Strength requirement of this designation is 14 x 145 = 2030 psi.
Tensile strength is the maximum tensile stress reached in stretching a test piece (either an O-ring or dumbbell).
Tensile tests are used for controlling product quality and for determining the effect of chemical or thermal exposure or an elastomer. In the latter case, it is the retention of these physical properties, rather than the absolute values of the tensile stress, elongation or modulus, that is significant.