Tudor Black Bay 58 GMT Jubilee 39mm 7939G1A0NRUOverview The Tudor Black Bay 58 GMT 7939G1A0NRU ("Coke") is the Black Bay 58 with a true flyer GMT complication the local hour hand adjusts in one hour increments without stopping the movement, packaged into the same 39mm, 11. 7mm slim profile case as the standard BB58. That complication in that case size, with COSC and METAS dual certification, at this price point, is the specification argument. No other manufacture currently delivers this