This cap comes from an insulator used on the Indo-European telegraph line. The insulator itself was like the one on the following drawing: http://www.gracesguide.co.uk/images/thumb/d/d0/Im1869EV8-p116.jpg/577px-Im1869EV8-p116.jpg There are remains of porcelain and some sort of cement inside the cap. The shed may have shattered due to mechanical strains experienced during thermal expansion-contraction cycles. Such strains appear due to improper selection of cement's thermal expansion coefficient. The eccentric that held the wire is completely missing, too. Probably snapped off due to galloping or during maintenance.