Hmmm..funny you mention this, as i am in the process of wiring my 1977 Lincoln Town Car to pull my 1969 23' Safari.
I purchased this same Pollak 7 way flat blade plug and was surprised to see that 6 out of the 7 plug ends were this way. The center post (yellow wire/spare) seems to have a round end lug that you strip the wire, and shove it in all the way whilst tightening the screw, and you have a very solid connection--almost impossible to pull out.
I stopped at our local RV superstore just yesterday and inquired about this, as I just don't particularly like the thought of all those closed loop solderless crimp terminals crammed in there.... I picked out a "Bargman" 7 way plug, and for kix n giggles the parts guy removed it from the package, took it apart and showed me that it had the exact setup as the Pollak brand.
So then I spied on the shelf a Velvac plug out of cast aluminum, and it had the 7 round lugs on the back that you shoved the bared wire end in and tightened the screw...(much like a circuit breaker box)...but wouldn't ya know, it was for a 7 way ROUND pin setup..... (not the 7 way flat blade ) ....AND it was almost $40 bux!!
Hmm..so it's back to the drawing board......hmmm....