WW1 On War Service 1915 munition workers numbered badge

A good original First World War official 'On War Service 1915 munitions workers badge', Crowned oval title, the voided centre bearing the 'Board of Ordnance' shield; the reverse with maker's details stamped in relief 'J.A.Wylie & Co London' 'U' and impressed with official issue number '32186'. Very good condition, retaining original buttonhole fitting. Height 43mm.