A pressure cylinder, such as a master cylinder or wheel cylinder for an hydraulic vehicle braking system, has a plastic moulded body (1) within which a threaded insert (5) is engaged and restrained rotationally and axially. A seal (14) is positioned within the body between surfaces of the insert and body. The insert provides a seat (10) against which is clamped, in use, a corresponding seat on a flared end (11) of a pipe (7), the latter being retained within the body by a pipe nut (8) threadedly engaged with the insert. Long-term thread torque and clamping force are sustained by the insert rather than by the plastic body which can be subject to "creep".