Question: I have a concrete floor and I made two holes to bolt a 1/4"-thick steel plate. The problem is that the steel plates haven't been drilled yet.

How can I determine where the holes will be drilled in the steel plates so they match the holes in the concrete?
[![enter image description here](https://i.stack.imgur.com/1Kt5n.png)](https://i.stack.imgur.com/1Kt5n.png)

Answer: 
The usual methods are:

1. Careful measurement. Really this doesn't need to be that precise, you are not looking for a press-fit between bolts and clearance holes.

If it goes wrong, just elongate a hole into a slot using whatever tools you have to hand (e.g. a round file, clapped-out old Bridgeport, ...) - Remember: "A grinder *file/filler* and paint make me the welder machinist I ain't".
2. Put pointy or painty things into the holes then press the steel plate down in place to mark it. In the dead-tree-carcass world there are things called "dowel pins" used for this kind of thing.
Do you really need to use the holes drilled in the concrete?

If not, pick another pair to be drilled far enough from the original ones. Make the hoes in the metal sheet first, put the sheet in position, secure it from movement and mark the spots or drill through the holes in the concrete.

Another point to be taken is how much the holes shall be coaxial. If the misfit can be in order of milimeters you can measure the position with a scale. If it must fit perfectly, two extra holes are a good tradeoff.