ALM do not stock the cover nor bump head for the SBC33N1 , as it is a left handed thread, they only stock and supply the inner spool.
Niether do GHS or EINHELL.
I have tried to find , but alas it would seem I am now the proud owner of A completly useless Spear & Jackson SBC33N1 , along with everybody else who purchaced one last year from ARGOS , as they no longer stock them either.
Dave, June 2011