MTD 300 Series Operator's Manual page 14

ReplacingShearPins
The augers are secured to the spiral shaft with two shear pins
and cotter pins. If the auger should strike a foreign object or ice
jam, the snow thrower is designed so that the pins may shear. If
the augers will not turn, check to see if the pins have sheared.
See Fig. 5-2.
Figure 5-2
CAUTION:
NEVER replace the auger shear pins with
anything other than OEM Part No.738-04124A
replacement shear pins. Any damage to the auger
gearbox or other components as a result of failing to
do so will NOT be covered by your snow thrower's
war ranty.
WARNING! Always turn off the snow thrower's
engine and remove the key prior to replacing shear
pins.
SECTION S -- OPERATION