A glass network of N atoms with n(1) of the atoms with a coordination number of 1, and m(2) of the atoms with a coordination number of 2 about which the bond-angle constraint is broken, will in general display a stiffness threshold (rigidity percolation threshold) when the average coordination increases to a critical value [r](c) = 2.4 - 0.4 (n(1) - m(2))/N. Silica and sodium tellurate glasses provide model examples for which this general relation predicts the observed rigidity percolation threshold; this relation predicts the percolation threshold only if one includes broken bond-bending constraints due to bridging oxygen in the former network and nonbridging oxygen in the latter network. The rigidity percolation threshold in (Na2O)(x)(TeO2)(1-x) glasses is observed to occur near x similar or equal to 0.18 in tellurium-125 Lamb-Mossbauer factor measurements.