|Concrete parting tool.
This is a tool used to create the sort of line you see in sidewalks about every 4-5 feet. After the concrete is partly set, but still soft, you run this tool along a straight board held over the concrete, forming a neat line with rounded edges. The purpose of this line is to weaken the concrete along that line, so that when the concrete cracks, it will do so at the bottom of the scribed line, where you won't see the crack. (With concrete slabs larger than a certain size, it's not a question of if, but when, it will crack. Better to have neat-looking, regularly spaced lines that look like you meant for them to be there, than irregularly spaced cracks that look like obvious defects. It's purely a question of hiding flaws, nothing that actually improves the performance of the concrete.)
This tool says on its label that it's made of zinc, and the surface looks a lot like zinc to me. It's quite heavy, presumably to make it easier to push along the concrete without riding up. Alloys referred to as "pot metal", which often contain zinc, are commonly used to cast simple shapes like this which don't need to be particularly strong, but this one claims to be all zinc, which is unusual and makes me think maybe it is. No idea why this would be better than pot metal: Maybe it's cheaper.
Source: Hardware Store
Contributor: Theodore Gray
Acquired: 28 October, 2005