Brass compression fittings. BS 864-2:1983 or BS EN 1254:1988. They conform to both these standards apart from marking: a fitting conforms to the standards with which it is marked.
https://www.bes.co.uk/54-mm-x-42-mm-reducing-set-17743/39737Compression Reducing Set - 54mm x 42mmhttps://www.bes.co.uk/media/catalog/product/5/4/54-mm-x-42-mm-reducing-set-imported_min_17743_P_1.jpg6.696.69GBPInStock/Pipe Tube & Fittings/Pipe Fittings/Compression41671241424145<p>54 mm x 42 mm reducing set.</p><p>Brass compression fittings. BS 864-2:1983 or BS EN 1254:1988. They conform to both these standards apart from marking: a fitting conforms to the standards with which it is marked.</p>BESt range00https://www.bes.co.uk/media/catalog/product/5/4/54-mm-x-42-mm-reducing-set-imported_min_17743_P_2.jpghttps://www.bes.co.uk/media/catalog/product/5/4/54-mm-x-42-mm-reducing-set_min_17743_L_1.jpg5056198111450add-to-cartfacet_type:Reducing Setspecial_price:6.690000cat_multi_facet_l1:Fittingsmore_sizes:17734,17735,17736,17737,17738,17739,17740,17741,17742products_related:17202,16444,23384,10138,9551,9564,9581,15240,13596,23200,7798sku:17743FittingsReducing Set17734,17735,17736,17737,17738,17739,17740,17741,1774217202,16444,23384,10138,9551,9564,9581,15240,13596,23200,7798177436.690000No{"Standards":"BS 864-2:1983","Connection":"Compression","Finish":"Brass","Fitting Type":"Reducing Set","Material":"Brass","Size":"54 x 42 mm","Type":"Reducing Set"}ReducingBESt rangeBrassMetric54 x 42 mm