This is how a shackle was designed to be done up,That is why it has the hole in the pin.It is not a good idea to tighten the pin as all it does is close the shackle like a spring and makes it hard to undo.
just do it up firm and twist the very thin wire.
People not using wire is the reason that shackles are not allowed at the trailer end.But Hammer locks are.

[color=#FF0000]Please post any comment into the exiting thread in Bright ideas[/color].

That comments thread is here,
http://www.candm.com.au/forum/viewtopic.php?f=15&t=8222