The torque that needs to be applied for this joint to break.
When a joint tries to constrain a Rigidbody2D it may need to apply torque to do so. This is known as the reactionTorque. Each physics update, the breakTorque is compared to the reactionTorque; if it exceeds it then OnJointBreak2D is called with a reference to the joint that broke. Knowing the joint that broke you can check the actual reaction torque that broke the joint using reactionTorque or GetReactionTorque.
The break torque can be set to Mathf.Infinity to make the joint unbreakable by any amount of reaction torque. You should use this if you never intend for the joint to break with torque as it indicates that the joint should not be checked each physics update, therefore provides better overall performance.
Note that breakTorque is not available on DistanceJoint2D or TargetJoint2D.
See Also: reactionTorque, GetReactionTorque & OnJointBreak2D.