Pre-print presenting an empirical ansatz in which the adjacent-generation mass ratios of all twelve Standard Model fermions decompose into products of seven specific odd primes and powers of 2. Five physically motivated conditions select the prime set {3, 5, 7, 11, 17, 23, 29} uniquely by exhaustive enumeration, with no free parameters. The construction reproduces quark ratios within ~2σ, charged-lepton ratios within 0.1%, and predicts neutrino mass ratios of 7/3 and 21/4 consistent with oscillation data to 0.4%. The relationship to Kirchhoff elliptic vortex stability is noted as a structural parallel.