i use these swivels to connect florocarbon leader to my main line -their small size(smaller than any other barrel swivel of equal test rating) is their outstanding attribute-and they are very strong-highly recommended if you like small swivels.
Well constructed product that falls between pedestrian crane/barrel swivels and the much pricier ball bearing alternative.
I use the #8s for pannie and walleye/bass rigs and they still have plenty of strength for the occasional pike. The #6s due duty for pike ice rigs and the #4s wind up on my musky leaders. Small for their strength, smooth turning and priced reasonably, they are a great product.
And no, I get nothing from SPRO. Just a true believer sharing my experience. Left this as I ordered 3/50 pks.