Do I need a fork terminal to install #8 into an 38660 Molex Barrier Strip?
That part you linked specifically says it has a captive plate. This is a plate which looks like a square washer with ridges in it that is wide enough to reach all the way to the walls on either side of the screw. It is used to give the screw a wide area to clamp down onto the bare end of wire and to ensure that all wire strands are clamped and secure no matter how far the they splay out when you tighten the screw. This second part is really important and the main reason why you really shouldn't just use a plain screw to tighten down a wire.

Your particular model has slightly curved plate to match the round contour of the wire. That's what that little curved piece of metal is is under the screw in the photo. The curved nature of your captive plate (which I have never seen before) makes it so your block actually works better with a bare end of a wire and not so well with a terminal connector. Usually they are flat so work equally well either way.

In cases where you have no plate, you can get away with adding a large washer, but it's not as reliable since the washer's chord (in the mathematical sense for circles) near the walls edge is so small that there is almost no material to contain the loose wire strands. Even less reliable is no washer and I never recommend that since at least half your wire strands will end up splaying out and be loose. But if you're in that scenario then you might as well just use a ring or forked/spade terminal instead.