True story.
A lad I worked with decided that he would get his own one of these -
- it's a thin, stainless steel sheet with various shaped holes and slots punched out of it. Its purpose is to allow you to rub out small errors on a drawing without disturbing nearby stuff that you wanted left. He was fed up with trying to borrow other people's ones all the time.
So, he set off into town, believing that W H Smith would be the most likely source. He took his place in the queue at the pen desk that used to be in the back corner and waited for his turn.
When his turn came, he suddenly realised that he had no idea what the correct term for it was, so he asked the poor young girl behind the counter "Do you sell rubber protectors?"
She became totally mute and just stared at him.
The bloke behind him in the queue told him "I think you want Boots across the road, old chap".
So, he had run out of lunch hour by now, and didn't think Boots would have one.
On returning to the office, he demanded to know what the correct terminology was, and this ended up with the truth coming out - up to that point, he hadn't really realised what he had apparently asked the poor girl for...
The generally accepted term would be 'eraser shield'...