What is it? And why don't you have one?

Beats me...maybe a guide of some sort for alignment of machinery bolts/parts for layout.

Groz Tools

"Centre Square"

You didn't say no googling.

Looks like it would make a great ninja weapon.

It's a micrometer.

Stephen

Yep...anchor bolt center finder for as-builts, that's a nice one, mine was plastic. 😛

Bolt centers

> Beats me...maybe a guide of some sort for alignment of machinery bolts/parts for layout.

It's designed for marking the centers of round stock, but I'll bet it would be good for marking the centers of bolts, by intersecting two center scribes at roughly ninety degrees.

Center Square

I purchased mine from Rocklers. $27 delivered in two days.

http://www.rockler.com/search_results.cfm?srch=usr&filter=center+square

Made of hardened steel it should last a career or two.
It will find the center of any shape, including my favorite massive bolts.

That's the smallest my foot has looked in decades...

In the second pic you can see the remains of a previous surveyors work in finding the center of the bolt. Think his location will meet tolerance?

Center Square

Prolly a good 1/8"-3/16" difference there!

Center Square

I'm embarrassed to say I've never seen one before. I usually made a template with a flat washer and string, then a dot with the sharpie, much faster than measuring and hatching each one.

Center Square

I have one I use for wood working and I find the following procedure is best and I would suggest you do the same. Draw your lines from all 4 quadrants and you will probably end up with a small square in the center which will give you a more accurate center.

The reason being is that while the edge of the center line is going to be dead on, your marked line will all be off to one side.

Center Square

Never seen one before, not embarassed about that and I will never need one.

I do have one

Mine looks like this, but it works the same way.

My guess is the proverbial 0.04' might matter on that site.