Ok, I've trawled through the box and the closest I can find are these two. Excuse the dodgy pics:
[IMG]http://img.photobucket.com/albums/v169/jazza42uk/Mobile%20Uploads/PSX_20160607_123216_zpsfmlgyr2t.jpg[/IMG]
Close-up view:
[IMG]http://img.photobucket.com/albums/v169/jazza42uk/Mobile%20Uploads/PSX_20160607_123323_zpsyd9iop8u.jpg[/IMG]
They are 17mm tall and the general description sounds like yours, as you can see the side grooves peter out towards the bottom. These came off my old Status when I blinged it up Let me know via PM if you want these, and I'll stick them in the mail. I'll clean them first
I've not got many spline shaft knobs in the box, I must admit. I have a few sets of three grub screw fix ones in black if you're interested.