These are rubber plugs that fit into the nozzle of the Brother GT-541, 782 GT-341, GT-361 and GT-381 Ink bags. These are replacements in case your existing one has been used too many times or if it's dirty beyond cleaning. These can be used with both the 250ml, 500ml and 250ml and 380ml Cartridges and bags. Brother refilling syringe kit is here
Watch our video on refilling the 500 ml Brother Ink Cartridges for your Brother GT-541 and 782 Garment Printers