Pen & Pencil Top Eraser Heads

That's different.

"These pen-or-pencil-top rubbers look just like the caps that go on ball-point pens, but they work just like normal erasers. So they're sort of retro and sort of useful and sort of squidgy and just the sort of thing that every pencil case should have." 

I wouldn't argue.

Pack of 10: £4.98.