So I'm working on a project that I want to attach to my bike by replacing the handlebar clamp on my thread less stem.

However I am wondering if there is a standard spacing for the 4 bolt clamps used on stem?

My research hasn't given me anything conclusive but I do notice a number of stems appear to have the same spacing.

Anyone know?

As far as I know, there is no industry standard.

Why not err on the safe side and replace the whole stem instead of just the faceplate?

No standard I have ever seen. Why wouldn't you just measure the cap you have? With calipers, it is one of the easier parts to measure. Measure outside to outside of holes, and subtract 1 hole diameter. For exact measurements, you can even fold in the diagonal measurement as a check. You can measure the threaded side as well, but then you have to figure out tap drill size to subtract. Clearance holes are much easier.

Yea I've measured my stem and modeled up a clamp to fit but I would like to make the piece universal.

I think I've figures out a way to do it but I need to figure out if the vertical spacing is the same. Not worried about the horizontal at the moment.