The plugs can be piggy backed with other 4mm plugs and fit cable up to 4mm in diameter. 1000pcs Gold Plated Copper BFA Z-Type 4mm Banana Plug Speaker Cable Connector. Qty 1000 pcs 100% Brand new, never used, High quality 24 Gold-Plated BFA z-type 4mm Banana Plug These 4mm plugs are constructed from a tough low mass, gold-plated copper alloy conductor, ensuring a consistently high level of performance and connectivity.