Two years ago I did a lot of work looking into Radco built front blowers used by Kubota and John Deere.
I wont repeat the extensive dialogue again but in summary, there were a variety of shear bolts issued for this style of blower protection. Some bolts had grooves cut around them to weaken the bolt.
These are a sample of the weaken bolts. These are for the Auger but the same design was for the fan.
Finally Radco introduced an upgrade which is the black flange and different shear bolt location.
Some knowledgeable dealers were doing upgrades for the customers with the "through the shaft" shear bolt.
As the upgrade entered production, the new flange was again orange for Kubota and Green for John Deere.
What became apparent was that owners who experienced multiple shear bolt failures ended up with deformed holes for the shear bolt which only made things worse. For owners who had the fabrication skills to weld up the holes and then re-drill a fresh hole, the problem ended.
Note in post #42 from this forum, the owner is using my pictures to explain how his problem was solved.
https://www.tractorbynet.com/forums/kubota-lawn-garden/280620-gr2120-yea-nay-5.html
Dave