In order to protect the knife the gear-box and various other aspects of the Knife drive train from damage due to over-loading,
a number of machines are fitted with an "Overload safety device" termed a - Shear Bolt.

The guillotine manufacturer calculates the "Shearing Force" required to fracture the Shear Bolt, then modifies it,
and so in this way the guillotine is protected from severe damage during an overload,
because the Shear bolt snaps which effectively disconnects the mechanical drive to the Knife Beam.  

It is therefore very important to the safety of the operator and the machine that only the Correct Shear Bolt is used for a particular machine,
a Shear Bolt should never be replaced with an ordinary high speed steel Bolt.