I recently acquired this Master combination padlock from Ebay to practie shimming with and I notice it has a keyway on the back of the lock.
http://www.tsiolkovsky-creations.co.uk/stuff/1974-1041.png
I am guessing that somewhere there is a key for this - probably only 'issued' to the school supers so that they can remove padlocks left at the end of the school year but I'd like to know if I am right in my suposition.
To be honest I've not tried picking it yet just in case it is used for something outre like enabling someone to reset the combination - which is probably wrong - but it would be useful to see if it is safe before I do anything I'd regret.
Rik