A fitting assembly (100, 1710, 1810) for coupling a first tube to a fitting body, the fitting assembly (100, 1710, 1810) comprising: a ferrule (120, 220, 320, 420, 520, 620, 720, 820, 920, 1020, 1120, 1220, 1320, 1420, 1520, 1620, 1720, 1820) having a nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629) and a bite end (137, 1037, 1137, 1237, 1337, 1437, 1537, 1637), and including: a reduced thickness portion near the nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629), the reduced thickness portion being thinner than adjacent portions of the ferrule and configured to flex when the fitting assembly (100, 1710, 1810) is made up; a thin section toward the bite end (137, 1037, 1137, 1237, 1337, 1437, 1537, 1637) in which an axially middle portion, between the thin section and the reduced thickness portion, is configured to bow radially outwardly during assembly of the ferrule such that a bite edge (138, 238, 338, 438, 538, 1138, 1238, 1438) and a portion of an inner surface (126, 826, 1026, 1126, 1226, 1326, 1426, 1526, 1626) opposite the bite edge (138, 238, 338, 438, 538, 1138, 1238, 1438), relative to the axially middle portion, are engageable with the tube, and the bite edge and the portion of the inner surface are configured to bow radially inwards towards the tube during assembly, and a nut (116, 1716, 1816) having a bearing surface (1751, 1851) for bearing against a bearing surface (1752, 1852) of the ferrule; characterised in that the reduced thickness portion has a radial thickness less than any other portion of the ferrule between the nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629) and the bite edge (138, 238, 338, 438, 538, 1138, 1238, 1438) of the ferrule, said bite edge being the closest bite edge to the nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629). a ferrule (120, 220, 320, 420, 520, 620, 720, 820, 920, 1020, 1120, 1220, 1320, 1420, 1520, 1620, 1720, 1820) having a nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629) and a bite end (137, 1037, 1137, 1237, 1337, 1437, 1537, 1637), and including: a reduced thickness portion near the nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629), the reduced thickness portion being thinner than adjacent portions of the ferrule and configured to flex when the fitting assembly (100, 1710, 1810) is made up; a thin section toward the bite end (137, 1037, 1137, 1237, 1337, 1437, 1537, 1637) in which an axially middle portion, between the thin section and the reduced thickness portion, is configured to bow radially outwardly during assembly of the ferrule such that a bite edge (138, 238, 338, 438, 538, 1138, 1238, 1438) and a portion of an inner surface (126, 826, 1026, 1126, 1226, 1326, 1426, 1526, 1626) opposite the bite edge (138, 238, 338, 438, 538, 1138, 1238, 1438), relative to the axially middle portion, are engageable with the tube, and the bite edge and the portion of the inner surface are configured to bow radially inwards towards the tube during assembly, and a reduced thickness portion near the nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629), the reduced thickness portion being thinner than adjacent portions of the ferrule and configured to flex when the fitting assembly (100, 1710, 1810) is made up; a thin section toward the bite end (137, 1037, 1137, 1237, 1337, 1437, 1537, 1637) in which an axially middle portion, between the thin section and the reduced thickness portion, is configured to bow radially outwardly during assembly of the ferrule such that a bite edge (138, 238, 338, 438, 538, 1138, 1238, 1438) and a portion of an inner surface (126, 826, 1026, 1126, 1226, 1326, 1426, 1526, 1626) opposite the bite edge (138, 238, 338, 438, 538, 1138, 1238, 1438), relative to the axially middle portion, are engageable with the tube, and the bite edge and the portion of the inner surface are configured to bow radially inwards towards the tube during assembly, and a nut (116, 1716, 1816) having a bearing surface (1751, 1851) for bearing against a bearing surface (1752, 1852) of the ferrule; characterised in that the reduced thickness portion has a radial thickness less than any other portion of the ferrule between the nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629) and the bite edge (138, 238, 338, 438, 538, 1138, 1238, 1438) of the ferrule, said bite edge being the closest bite edge to the nut end (129, 1029, 1129, 1229, 1329, 1429, 1529, 1629).