The combined theory of Special Relativity and Quantum Mechanics (c-SRQM) suggests the existence of a Primordial Stem Particle (PSP) whose rest mass m_bar is thought to be the cutoff limit for massless particles. At its condensed state of various quantum energy levels, the PSP is thought to be the sole constituent of black holes singularity, and in its free state, the PSP is thought to permeate the entire universe as a relic left from the Big Bang. The c-SRQM theory also suggests a physical limit a_u=c^2/A for acceleration, and with that, arrives at the concept of the Unit Black Hole (UBH) with mass M_1=A c^2/(4G) whose gravitational pull at the event horizon of diameter A is equal to a_u. The PSP constituents of a stand-alone UBH have the spatial uncertainty delta_x=A, thereby confining the particles to the very surface of the UBH event horizon. For larger black holes with index b>1 and mass M_b > M_1, a layered internal structure emerges comprising of b concentric spherical shells. The quantum index of constituents of each shell matches their shell number: the innermost shell 1, ie. UBH, is occupied by the PSPs at quantum energy level n=1, the following shell 2 is occupied by the PSPs at quantum energy level n=2, and so on until the outermost shell b which is occupied by the PSPs at quantum energy level n=b. These concentric spherical shells create the core or the physical singularity of black holes, a structure somewhat similar to but far simpler than the electron shells in the atomic structure of ordinary matter. A set of LIGO-Virgo Gravitational Wave data is used to constrain the UBH mass median to 7.402E23 (kg) and its core diameter to 2.197 (mm). The resulting PSP mass is constrained to a median of 1.006E-39 (kg).