Ummm.. my grub screw required an allen key
I still don't know why I had to modify the cap to make it fit. Everyone elses seems to fit fine yet the dizzy stub for locating the cap was on th opposite side to the cap.
My SiR is a bit older than moppie's, but in theory it should be the same design.
Moppie: I might take a pic of mine tomorrowand post it up for you to look at.
Cheers