I recall when I was at primary school in the late 1960s first seeing one of the early issues of Renniks with an image of an interesting shilling variety; that of a 1961 shilling with a vertical bar on the wool (left image below). Over the next forty years I examined every 1961 shilling I encountered without finding one that matched the Renniks coin, although, as I'll describe later I found several that at first glance appeared to be the real thing.
It was not until the middle of 2007 that I finally obtained one in a bulk lot at Downies' Australian Coin Auctions (image on the right). The bar is in the same position and at the same angle (vertical!); but the bar appears less well defined. It is difficult to be certain as to the reason but it may just be that mine is a later strike and that further damage to the die has widened the bar, or the apparent difference could just be due to differing imaging processes.
Now for the look-alikes. The "true" or Renniks bar in the wool has the bar starting slightly to the left of the second upright of the N and is vertical.
Below you can see images of the three look-alikes I purchased at various times. I find it interesting that if we assume the 'bar' is due to die damage then all three appear to have struck by different dies. I can imagine that die failure in the same area can occur on a number of working dies (the decimal equivalent is the weakness on the dollar coins that gives the "rabbit ears" variety; it is known on a number of different issues), but apart from uncomfirmed reports of a 1960 bar in the wool shilling, why don't we see this on other years?
In conclusion, the "true" 1961 bar shilling has the bar starting just to the left of the second upright of the N and is vertical. Accept no substitutes. And if your ever find a 1960, you know who to call....