What Spade Size to Use on B&W 803S Binding Posts

I am trying to buy a set of custom speaker cables. What size spades should fit perfectly on the binding posts of B&W 803S speakers?

The binding posts are WBT--0765. The specs state it would take 1/4" or 5/16". But I doubt that either one would fit because of the opening of the external plastic slot. I am afraid that the spade would not fit in the opening before it reaches the actual binding post. I hope I described it correctly.

I am using the 5/16" spades on my Kharma loudspeakers with the same WBT ( with plastic slots ) and had no problem getting them to fit...Its a tight squeeze but managed to get them in..You could hand file off the spades sides slightly if neccassary or even open up the slots a bit if needed...Some people remove the WBT plastic housing completly ...Git er done.....Not that big if a deal,,
On my B&W 803D, I use Kimber WBT 0681 spades 5/16" and the plastic slots would also take 1/4".
I have the same issue with my KEF speakers. Any idea how to remove the plastic housing without completely destroying it?