Hello Carl007,
Welcome to the HP Support Forums!
Unfortunately neither the 8500 A910 nor the 8600 N911a support printing banners. The longest media either support printing is legal (8.5x14).
The printing specification for the printers can be seen here: HP Officejet Pro 8600 e-All-in-One Series Printer Series (N911) Product Specifications& HP Officejet Pro 8500A (A910) e-All-in-One Series Printer Product Specifications.
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