I recently dug out an old Hurd padlock that my grandpa gave me fifteen years ago. I did a search for "Hurd" on this site and didn't come across much, so I thought I would contribute something new. I have yet to locate the key, which I have laying around somewhere. The first thing I figured out from picking it was that on this padlock the key is rotated 90 degrees counter-clockwise to release the shackle. What is also interesting about this lock is that there is no visible notches in the shackle when it is released. This would mean that some sort of internal and inaccessible mechanism secures the shackle. It also utilizes five pin stacks and perhaps the simplest keyway I have come across. I find this rather unusual, considering the heftiness of this lock (it weighs substantially more than my American 5200). From what I could ascertain when picking it, none of the stacks appear to utilize spools or any other sort of security pin. This lock is key-retaining.
Pictured below is the Hurd lock on the right with an American 5200 on the left to give viewers an idea of how large this lock is.

Also, here is a view of the keyway in the picked position. You can see that it uses a metal cover to protect the keyway from the elements.
