Enclosure (16) for housing a coupler (18) between a driving rod (20) and a driven rod (22) comprises a first and a second preferably cylindrical pieces (30, 28). Said pieces are sized so that the first piece (30) is able to slide telescopically within the second piece (28) and are threaded to engage each other when in operation the enclosure (16) is in a close position, thereby the enclosure (16) being able to retain lubricant in the inside. For service, after having drained the lubricant from the enclosure (16), the two pieces are loosened by screwing the first piece (30) until the end of the thread is reached, and then the first piece (30) is slideably telescoped into the second piece (28), thereby setting the enclosure (16) in an open position an enabling easy access to the rod coupler (18).