
Eraser shields like this, most useful with a motorized eraser, was a standard drafting tool for decades. It does not rust, and unless it gets bent up, should last a long time.
Having done hand drafting, I have wondered why the shield had this particular pattern of shapes. Some make obvious sense, like the circle, the teardrop, and the various straight line strips of various lengths, but some of the others are rather odd, and I rarely used them. There are many round edges, because a sharp edge would tend to wear down the eraser more, but there are times when a nice square corner really comes in handy. Why so many circles of the same size, when you just need two circles to make an evenly spaced dashed line? A few more circles of different sizes, and a square or rectangle or two, might have been useful additions.
Too many cutouts in the metal would make the shield prone to bending, but it doesn't seem that much thought went into the selection of the pattern of shapes, and surely more shapes could have been added. As a result, for many decades those involved in fields like engineering and architecture, had to make do with a product that very easily could been made more useful. All that lost productivity! Well, it's too late now, as hand drafting has largely become a thing of the past.
If you do hand drafting, this is still a good tool to have. As with many drafting supplies available thorough Amazon, the shipping charge is a killer, so you might want to check at your local graphic arts store.Get more detail about
Quint Graphics Stainless Steel Erasing Shield.