What size is a FedEx bike box?

Excuse me, could you please clarify the dimensions of a FedEx bike box for me? I'm planning to ship my bicycle through their service and I want to ensure that I have the correct packaging. Are there specific size requirements for the box, or do they provide different sizes to accommodate various bike models? Additionally, could you elaborate on any specific instructions or recommendations FedEx might have for securely packing a bike in one of their bike boxes? Your insight would be greatly appreciated.