Please check the diagram of the RCX H2206 and RCX H2208 Motors, then you will see.
CCW Prop Mount With Silver Bullet
From Nov 2014. We have changed the color of the CCW Bullet to Silver for easier to distinguish. So it looks like below.
** The only difference of the Prop Mount between H1806 and H2206 are the shaft diameter hole. H1806 is 2mm but H2206 is 3mm. So basically, H1806 can use H2206 Prop Mount (because 2mm shaft can go into 3mm hole) but H2206 cannot use H1806 Prop Mount.