This branch is defined by the Y-Haplotree at FamilyTreeDNA as I-BY421. There, it is the child of the I-L596 branch.
BY421, BY16355, BY16356, BY16357, BY16358, BY16360, BY16370, BY16373, BY16381, BY16387, BY16389, BY16390, BY16391, BY16395, BY16396, BY16401, BY16404, BY16406, BY16407, BY16410, BY16412, BY2803, BY2804, BY2805, BY2817, BY420, BY422, BY423, BY4301, BY48421, M4099, PH1912, PH2569, PH2849, PH2860, PH2930, PH3525, PH3539, PH3653, PH4144, PH4230, PH4607, PH5443, S6800, SK1270, SK1271, SK1273, SK1274, SK1275, SK1276, SK1277, Y16419, Y16420, Y16421, Y16422, Y16425, Y16426, Y16427, Y16428, Y16429, Y16430, Y16649, Y16650, Y16651, Y16652, Y16653, Y16655, Y16656, Y16657, Y16658, Y16659, Y16660, Y16663, Y16666, Y16668, Y16669, Y16670, Y16671, Y16672, Y16674, Y16675, Y16677, Y16678, Y16679, Y16680, Y16681, Y16682, Y16684, Z26373, Z26375, Z26376, Z26377, Z26379, Z26380, Z26381, Z26382, Z26383, Z26384, Z26385, Z26386, Z26387, Z26388, Z26389, Z26390, Z26391, Z26392, Z26394, Z26396, Z26397, Z26398, Z26399, Z26400, Z26401, Z26404, Z26405, Z26407, Z26409, ZS2741
I am working on linking information from the public YFull tree. This branch is not linked yet.
Peer reviewed sources have not been added for this branch yet. If you know of one I have missed, please link to it in the comments.