Question about Fitting Z Plugs to Speaker cable??

First off I should say I'm new to this so sorry if the termionology is off.

I have these LFD Z plugs. The way they work is you fit the bare wire in to the plug and screw it down with two set screws, no crimping and no soldering, then the LFD metal casing screws on top of that for cosmetics.

My question is, won't the wire eventually oxidize becaue it is not air tight.

For a pic of the plug I included a link below:

http://www.divinecables.co.uk/itemdetails.php?itemId=149&itemId2=speaker-terminal-banana&PHPSESSID=f78364fee9e709fdd344fad20e7624d1