The Anti Chain Suck Device bolts on to the Bosch motor unit. It surrounds / protects the driver sprocket, prevents building-up of mud and avoids chain-lock issues on the chain transmission system in extreme muddy conditions.
This item is for the (BDU2XX) Bosch Gen2 ebikes motor units
This device bolts in directly on the Bosch BDU Gen2 bare alloy case and will always fit on the Gen2 alloy case on its own... however there are bike manufacturers that are adding plastic covers to the case causing interference with ACS (if this is what you have on your bike) in order to fit the ACS device you would need to remove the plastic cover (usually these are just cosmetic covers) and ride it without the plastic cover, furthermore in some rare occasions more serious interference problems have been found with unusual frame design, or chain tensioning systems, or orientation of the BDU on the bike... making the use of the ACS device, not possible or not recommended.
(NOTE: THE 5x PICTURES OF DEVICE FITTED and NOT FITTED ON MOTOR UNIT ARE FOR VISUAL REFERENCE ONLY)