This is one bolt and nut (I don't know, diameter of the bolt is about 10cm so something like M100 even though it is probably not metric) connecting the "chain" to the actual bridge of the Menai suspension bridge, the first iron suspension bridge built by Thomas Telford in 1826. It is spanning the Menai Strait between Anglesey and mainland Wales(580 foot) and it had to have a clearance of 100 foot to allow big ships to pass underneath. The biggest task was to lift the 16 chains into place because the middle section between the pillars has a weight of 23.5 tons per chain!!
Wales (Cymru in the Welsh language) is part of the United Kingdom of Great Britain and Northern Ireland. The major cities are Cardiff, Swansea, Newport and Bangor. The city of St. Davids is the smallest city in the UK with a population around 2000. Wales itself has a population of around 3 million. The Welsh language is spoken by around 20% of the population.