What is the thingie on the WBT Bananna Plug

I am looking at getting some bananna plugs, and in particular have noticed the WBT model 0645. It looks like it has an insulator or something plastic that protrudes from the front parallel to the bananna extrusion. Anyone know what this is? Looks like this will prevent the bananna portion from going into the receptacle, will it?

Also, any comments on this plug, where to get it, or other comparable connectors. Please, Bananna only because that is all my speakers will take, the have 4 bananna holes per speaker (no "spades are better" please because I can't use them).
Here is the wbt cite

http://www.wbtusa.com/wbt0645.html

Thanks in advance for your helpful comments and/or jokes!