New Heyco 7K-2 cord grip Snap in Plastic strain relief lot of 20 pcs.  New never installed.  

According to the Heyco site these fit cable diameter .325" to .360". 

They list cable size 16/2, 18/3, 14/2, 16/3, and 18/4

I have many of these and will be happy to combine shipping is you need several.