regard the thread means of the fastening member 306 may be adapted to engage the thread means on the external surface of the second annular pipe member 302 when the pipe union 300 is closed as illustrated by the thread connection 362 in fig3 a during an exemplary installation of the pipe union 300 the annular pipe members 304 and 302 may be attached to the corresponding lengths of pipe by for example utilizing thread means 360 and 358 the third annular pipe member 314 may then be disposed between the first annular pipe member 304 and the second annular pipe member 302 the fastening member 306 may then be slided over the first annular pipe member 304 so that the inwardly extending flange 307 abuts the flange shoulder 311 of the extending flange 309 of the first annular pipe member 304 the pipes union 300 may be closed by engaging the thread means on the fastening member 306 with the thread means on the second annular pipe member 302 resulting in thread means commection 362 the fastening member 306 may then be tightened so that the rear face of the first annular pipe member 304 abuts the front face of the third annular pipe member 314 in area 372 and the rear face of the third annular pipe member 314 abuts the front face of the second annular pipe member 302 as illustrated in fig3 a.