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/15-mm-x-12-mm-reducing-set-17737/39731Compression Reducing Set - 15mm x 12mmhttps://www.bes.co.uk/media/catalog/product/1/5/15-mm-x-12-mm-reducing-set-imported_min_17737_P_1.jpg0.610.61GBPInStock/Pipe Tube & Fittings/Pipe Fittings/Compression41671241424145<p>15 mm x 12 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/1/5/15-mm-x-12-mm-reducing-set_min_17737_L_1.jpg5056198111399add-to-cartfacet_type:Reducing Setspecial_price:0.610000cat_multi_facet_l1:Fittingsmore_sizes:17734,17735,17736,17738,17739,17740,17741,17742,17743products_related:20394,8748,18256,6921,9084,7621,16444,6962,21385,21031,7550sku:17737FittingsReducing Set17734,17735,17736,17738,17739,17740,17741,17742,1774320394,8748,18256,6921,9084,7621,16444,6962,21385,21031,7550177370.610000No{"Type":"Reducing Set"}ReducingBESt rangeBrassMetric15 x 12 mm