Looks just like a No.3 to me. Here's the page for it.
http://www.masterlock.com/business-use/product/3 . Any difference would be rather superficial.
"4-pin cylinder for added pick resistance" Holy hell they really grasp at straws when advertising. Must've added onto their good ol 3 pin design.
Edit: on second look, it looks like the 3D appears to be marketed towards home owners and the 3 marketed to commercial uses, given the customization they offer with different shackle materials and key control.
