I have a triple clutch jump trap made by the Triumph trap company. It is a #1 sized jump trap, with a cast jaw that has an extra set of inverted "T" shaped lugs cast into the underside of the jaws. They apparently were made that way to increase holding ability. I also have a couple of them in #1 size long spring. I am not a trap collector, but think that the #1 1/2 you mention is similar to these but just larger. Hope this helps.