Hello and welcome, I think your mower is an Atco. Looks to be missing it's rubber block that sits between the two claws

Have a look at this EBay auction, in the picture you are missing the part in the middle. It may be a rubber or nylon block.

http://www.ebay.co.uk/itm/Atco-B17-Commodore-EL-engine-to-drive-shaft-coulping-clutch-housing-/351627106914?hash=item51de9bda62:g:-RsAAOSwUdlWgSLY

The rest of the shaft would mount in between but the drive sprocket would be on the outside of the chassis. Hope this makes sense



Last edited by paul_c; 17/01/16 07:31 PM.