Its a through hole with a nut and just this bolt will fail if a hinged assembly takes an impact, this bolt needs to shear to limit tearing the assembly up. So really its a mild arc that will shear the bolt. Right now I have the stress groove located in the slight gap between the two plates.
I've busted a bunch of these when my snowblower eats rocks, pressure washer hoses etc.
The gears have not broken, yet, but the auger shafts are bent a bit.
The main drive is by belt off the engine, but if that slips, it does not slip enough to spare the shear pins.
Looks like most of those grooves are with a radius nosed tool, some v-grooved. I was just questioned whether shape of concentration had much of an affect on shear angle and couldn't remember all the specifics from materials and mechanics of materials or if it really mattered in this instance as long as my cross section was what matched my preferred fail load. Also inducing some heat and entering the center of a larger sized bolt, which might have a different crystal structure at its interior.
