Tudor Black Bay 58 39mm 7939A1A0NUOverview The new generation Black Bay 58 carried forward the 39mm case and slim profile that made the original BB58 the most wearable piece in the Black Bay family and upgraded the movement specification to a standard that few watches at this price point reach. The 7939A1A0NU is the three link bracelet configuration of that update, the BB58 in its most tool watch oriented form. The Calibre MT5400 U holds both COSC and METAS certification