Mossberg 500/590 Cartridge Interrupter

Have for sale an extra cartridge interrupter for a Mossberg 500 or 590 in either 12ga or 20ga. It came off a 500 field version in 12ga. It's in great shape and works as intended! No use for it, maybe you do?

Asking $12 shipped via lettermail! EMT is king! Thanks.