shear bolt revisited!!!!!!!

kco · Dec 15, 2016

My MK Martin 75" snowblower specifies different grades for bolts. The auger shear bolt is a 5/16" grade 2 while the Italian made Comer driveshaft which powers the blower and auger is a 10mm class 8.8. Metric 8.8 is similar to SAE grade 5 while metric class 10.9 is similar to SAE grade 8.

The metric class rating gives the actual tensile and yield strength for the steel as shown here:

Metric Class 8.8 Hexagon Bolts & Nuts 12mm AF

PILOON · Dec 15, 2016

I have always used grade 5 for years.
I get them by the 25's and my blower is none the worst, in fact only problems I ever had was using softer 'hardware store' bolts.
The softer bolts bend and mushroom the ends while the grade 5 shear nice and clean and less often.
Once in a bind I used soft bolt and actually had to drill it out.
Chunks of ice shear soft bolts while it takes a stone to shear a grade 5. (and generally it is one that gets wedged between the fan blade and housing.)