HAP40 is a tool steel manufactured in Japan. This makes it a candidate for knives made in the Spyderco Seki City facility that usually uses the Japanese VG-10 steel. Like most tool steels, it is not stainless, but can be sharpened to an amazing edge that it holds for a long time.
I generally avoid back lock knives, but thought maybe it was time to give one of these classics a try. But I was not sure whether I would want the smaller Delica or the larger Endura. My preference usually runs towards larger knives, but I was surprised when I want to a local store and tried both in my hand. I liked the Delica, whereas the Endura felt large and awkward. So between these two, the clear choice for me is the Delica with a 2.9 inch blade. Other people with other hands may feel differently. If I want a bigger blade, I can grab a Manix or PM2 or some other knife.
But then I found that the Caly 3 was also going to be produced using HAP40 and I decided to order that knife instead after reading reviews. Note that there is also a Caly 3.5, but not available in HAP40.
But if you are really excited about a 3 inch blade, the option that should not be overlooked is the new Paramilitary 3, which is not a revised version of the Paramilitary 2, but rather a 3 inch version of the same. A questionably choice of nomenclature in my opinion (what are they going to do when and if they revise the Paramilitary 2?). Note that the Paramilitary 2 has a 3.42 inch blade.
But as I wander far afield, I have to remind myself that what got me started in all of this is an interest in HAP40 steel, not 3 inch blades.
Tom's Knife Info / tom@mmto.org