The interfacial shear strength is a critical parameter for assessing composite performance and failure behavior. This parameter is usually obtained from a single-fiber fragmentation test that induces sequential fracture with increasing strain of a single embedded fiber with output being the distribution of fragment lengths. An exact analytical form for the expected fragment length distribution is still not known. Such data are often fit empirically to Weibull, shifted-exponential, or lognormal distribution functions. In this report, new insights into the sequential fiber fracture process are provided by detailed analyses of the fiber break locations along the length of the embedded fiber. From this approach, the high degree of uniformity of the break coordinate loci strongly suggests that there can be no mechanistic rationale for the use of the Weibull, or lognormal, or exponential functions to fit the fragment lengths. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2301-2312, 2009