Herdio Heavy Duty Marine Box Outdoor Speakers Can Install Anywhere Needed Herdio Heavy Duty Marine Box Outdoor Speakers Can Install Anywhere Needed All four speakers need to be connected to yours amplifier or receivers before they can be used. Amplifier and receiver are not included in the package . How to connect and use the speakers？ All four speakers need to be connected to yours amplifier or receivers before they can be used. Amplifier and receiver are not included in the package . Is the grill cover of this speaker removable？ No,they can not be removed,but the bracktes can be flexibly rotated and disassembled. What size are the screws in the package？ The rotatable installation part of this screw is 3cm. Herdio 4" Marine Speakers Herdio 4" Marine Speakers Herdio 4" Marine Speakers Herdio 4" Marine Speakers Herdio 4" Marine Speakers Herdio 4" Marine Speakers Herdio 4" Marine Speakers