The Glock 26 is 26% thicker, 8% longer, 1% taller and 58% heavier than the G42.
I know people like to throw numbers around, but they really dont mean much, when you dont have them in your hands to compare.
I have all the models you mention, and have carried all of them, so I have a real good idea as to whats what. I also still feel the differences between the 17 and 19, arent enough to warrant giving up what the 17 offers over the 19. The 26 has the advantage of going where both the others cant, and yet, can actually come very close to "being" both the others, with a simple mag change. The 42 is just the 42.
Perhaps because Ive carried full size handguns most of my life, and second, and even third back up guns that many today, seem to consider full size, I have a different outlook on things and Im less sensitive to the differences in size, especially when you factor in what your giving up or gaining. I dont know how many times on this board and others, Ive been told its "impossible" to carry anything bigger than one of the sub, sub compacts, and that what I consider a "slight" difference, is in fact major. Hey, Im not a big person, and Ive carried it off daily now, for decades. Again, I seem to have a different perspective.
These days, I normally carry a 26 in a Smart Carry, or an ankle holster. Ive also carried the 42 in the same Smart carry. I saw no difference what so ever in doing so. That "slight" bit of extra thickness on the 26 is in no way a detriment, and the missing thickness on the 42, didnt stand out in any way. I suppose if Id carried the 42 first, I might have noticed the weight, but I really kind of doubt it would have mattered much after wearing it for a short while. Both are very comfortable in that holster. The 26 isnt uncomfortable in an ankle holster either, for that matter.
Heres a couple of pics of the two. I tried my best to show the difference in length with the 42 on top of the 26, but no matter how I tried to take the pic, it really doesnt show up. But yes, it is a little shorter, but as you can see, its not enough to really show up in the pic even.....
Trying to get a good representative pic of the thickness was a little harder. No matter how you do it, it seems one or the other gets distorted. This was the best I could do. Still, if you think thats "a big difference", you must be relaed to that girl with the pea under her mattress...
The same goes for saying that there's not much difference between an LCP and a G42. If you're going to carry either one IWB, I guess that's arguable, but if you're looking for a .380 BUG to stick in your blue-jeans pocket, there's no comparison. The two guns are in entirely different classes.
I dont carry any of my "little" guns, IWB, or in a pants pocket. No point IWB, and to much junk in my pockets. I do occasionally throw one in a coat pocket in colder weather. I actually find trying to hide a small gun in my pants pocket, harder, than I do my 17 IWB. Those Smart Carrys, do a much better job for the little guns, and actually work quite well, with guns many consider to be full size.
As far as the "different class" thing, the difference between my Seecamps and my LCP are more of a difference, than my LCP and the 42. The Seecamps are truly a "small" gun. I dont find the LCP to be all that small. When you actually consider shooting them, the LCP falls away quickly.
I wouldn't mind having a GLOCK 42. I would be more interested in a GLOCK single stack 9.
As I said before, Id be very surprised if we ever see one. The 26 basically has that covered.