First determine whether the padlock is single or double latched. If you
don't know, then start by sliding a single shim down the inside of the pivot
leg of the shackle to feel for a latch. Ideally, knowledge of the lock is the
best way of knowing whether it is a single or double latch.
For most padlocks, the latched leg of the shackle is generally on the same
side as the serrations of the key. Choose a shim having the same or slightly
larger bend radius than the shackle diameter. A slightly larger radius will
close down to the correct shape more accurately than an undersized one
will open up. It may also be necessary to shorten the length of the arms
before using a shim on smaller padlocks.
Exert some pressure on the pivot side of the shackle to ease the shackle
towards the latch side and increase the clearance between the shackle diameter
and the hole. Then insert the shim into the clearance on the outside
of the shackle opposite the latch and twist and push the shim down as far
as possible. When the shim is fully inserted, rotate the shim around the
shackle so that the tongue of the shim approaches the latch from the side
and eases it back. Once the shim had been rotated until the wings of the
shim are pointing outwards away from the lock, it is likely that the latch
has been sprung and the shackle can be pulled to open the lock. On some
types of padlocks with weak latch springs, it may be possible to force the
shim down onto the latch(es) directly from above, and ease it (them) back.
However, if this technique is used on a latch with strong springs, the tip of
the shim could bend and the latch would not be pushed back far enough to
release the shackle.
More detailed information about lock picking can be found in "The Beginner's Guide to Lock Picking" which is included with the Secure-Pro® Credit Card Lock Pick Set.