Forgefix cavity wall nylon speed plug forgefix msp420 these forgefix cavity wall plugs are made from zinc alloy and have a specially designed cutting tip to pierce the plasterboard skin cavity fixing plugs are an easy to use fixing for plasterboard and hollow wall applications they are supplied complete with a 4mm screw and the countersunk head feature on the plug allows flush fitting of the screw to the plasterboard the screw and fixture can be removed for cleaning and decoration altern