Locks that work

It did look a lot like the 54, but could have possibly been the granit 51, definitely none of the others. The 54 and the 51 have very similiar locking shackles.

But they are both 13mm bars, so why would the square bar shackle be more resistant against cutting? I thought it was just so you couldn't twist the shackle out.

This required a Maths answer, and the man for that is actually Tommy(TheBrick), but since he hasn't seen it, I've had to try to answer it myself.

If the circular bar has a diameter of 13mm, we can Imagine this:

But if the bar is square shaped then the 13mm width (as claimed by Abus) would give a through-diameter of 18.38mm (approx). The width of the square finds the diameter by multiplying the 13mm side by the squareroot of 2 (1.41421356...).

So even though the sidea are all 13mm, cutting at any angle at all, encounters 18mm of hardened steel.