There have been little items called strainserts around for ages. They are actually the bolt itself, fitted with a small strain gage. All us engineer dweebs have been using such stuff for decades. I'll bet even the Bureau of Standards even has a certified gizmo similar (costing about the same number, but add two decimal points you could buy to calibrate whatever you might have. They need to be hooked up to electronics to get a reading, and I believe this cool little number is just all of that in a wee small box. Needs batteries, i'm supposing. there is a Harbor Freight nearby, I should check it out. Great tip.