<P> The arch is composed of two 28 - panel arch trusses; their heights vary from 18 m (59 ft) at the centre of the arch to 57 m (187 ft) at the ends next to the pylons . </P> <P> The arch has a span of 504 m (1,654 ft) and its summit is 134 m (440 ft) above mean sea level; expansion of the steel structure on hot days can increase the height of the arch by 18 cm (7.1 in). </P> <P> The total weight of the steelwork of the bridge, including the arch and approach spans, is 52,800 tonnes (52,000 long tons; 58,200 short tons), with the arch itself weighing 39,000 tonnes (38,000 long tons; 43,000 short tons). About 79% of the steel was imported from England, with the rest being sourced from Newcastle . On site, the contractors (Dorman Long and Co .) set up two workshops at Milsons Point, at the site of the present day Luna Park, and fabricated the steel into the girders and other required parts . </P> <P> The bridge is held together by six million Australian - made hand - driven rivets supplied by the McPherson company of Melbourne, the last being driven through the deck on 21 January 1932 . The rivets were heated red - hot and inserted into the plates; the headless end was immediately rounded over with a large pneumatic rivet gun . The largest of the rivets used weighed 3.5 kg (8 lb) and was 39.5 cm (15.6 in) long . The practice of riveting large steel structures, rather than welding, was, at the time, a proven and understood construction technique, whilst structural welding had not at that stage been adequately developed for use on the bridge . </P>

Where did the steel for sydney harbour bridge come from