The Master Switch is a great by-pass tool For Classic Master padlocks #1,#2,#3,#4. 

It does not work on the current #3 as Master lock fixed the defect, however there are millions out there that are still vulnerable.  By inserting both switch's deep into the keyway of the lock you are able to open the padlock. With the assistance of some padlock shims you can even open Master padlocks #5,#6.

The Master Switch is just a fun tool to use. You might be just as fast to pick the lock open but there is something to exposing a built in weakness and using a bypass tool.

ALSO MAKE SURE TO CHECK OUT THE MASTER BLASTER ... it opens all Master #3's and the smaller Master #1's

MASTER BLASTER