The cross-arms (10) for electricity or telephone lines (13) are mounted on poles (11) by mounting brackets (12) so that the upper faces (17, 18) of the cross-arms (10) are inclined downwardly at approximately 45.degree. to the horizontal. The lines (13) are carried by insulators (14) whose bases (15) are bolted, screwed or clamped to the cross-arm (10). The cross-arms (10) are supported in substantially V-shaped cradles mounted on, or formed integrally with base plates fixed to the poles (11).