2 x Pli-Glass Ink Sacs for Vintage Parker 51 Aerometric Fountain Pens.
They are made from injection moulded PVC which Parker dubbed "Pli Glass". These very durable sacs were fitted to Parker 51's made from 1948 through to 1975. The price is for 2 x ink sacs, attach them to the nipple using clear nail varnish.