Below are most commonly stock freewheels.
Freewheels (or thread-on freewheels) are required for rear wheel gear replacement in an electric hub.
Large vendors like Shimano stopped carrying 11 tooth a while ago.
The 11 tooth listed below are custom manufactured for ebike, hence higher in price.
For most 13 or 14 tooth lowest gear is sufficient.
For BMC hubs 8 or 9 speed freewheels may require a small washer to allow for extra space in the frame.
Freewheels used to be more popular and diverse as a generic standard as opposed to vendor specific standards such as Shimano cassettes.

Freewheels
Click on photo to see larger image. This table is for ordering individual or replacement BMC parts. It is easiest to use BMC Configurator for Ordering Compete Kits here	Purchase
	Freewheel 7 Speed 11-28T Nickel FW7-11-28T $29.00 Quantity :
	Freewheel 8 Speed 11-21T Nickel FW8-11-21T $29.00 Quantity :
	Freewheel 8 Speed 11-32T Nickel FW8-11-32T $29.00 Quantity :
	Freewheel 9 Speed 11-32T Zinc Plated FW9-11-32T $35.00 Quantity :
	Freewheel 6 Speed 14-28T FW6-JB18431 $16.00 Quantity :
	Freewheel 7 Speed 14-28T FW7-JB18804 $17.00 Quantity :
	Freewheel 8 Speed 13-28T FW8-JB18599 $19.00 Quantity :
	Freewheel 9 Speed 13-32T FW9-SUNRACE $29.00 Quantity : Click here to see more product details.