They are called "hidden tang" knives.

They don't need a "guard" per se, but there really should be something in front of the handle otherwise it would look funny, to most people at least. You can use a ferrule or just a "bolster", which is basically a guard, but without the finger lug that extends down, or both up and down.
Here is a vid on an easy way to make a ferrule by a good friend of mine:
[video=youtube;46Ia-yUp-Z0]https://www.youtube.com/watch?v=46Ia-yUp-Z0[/video]
Also, there is a thread from a couple days ago that should be on the first page still since I just posted in it, titled:
Tight lipped guarded secret no pun intended (<--- click link to go there) that goes through pretty much everything ya just asked. Read that and I bet all of your questions will be answered. :thumbup:
I'll go ahead and copy & paste the reply I posted on that thread here as well:
"Here is the part of Nick Wheeler's AWESOME Tutorial/ WIP where he begins fitting the guard.. It starts on page 10, showing the importance of the ricasso shoulders and how they shouldn't be at a sharp angle and the inner corners of the tang section (due to stress risers) etc.. Here is page 10
http://www.bladeforums.com/forums/s...-s-Steel-*-Stuck-in-the-metal-with-you/page10
Then on page 11 is the actual guard making and fitting, and then page 12 goes into it a little more and then to the handle fitting, which of course is very much related to the guard, in making it all come together nicely, that is, as the final handle.. So yea, read page 10, 11, 12. Then go to page 1 and read the entire thing!

He goes into this a little earlier but it is important that the ricasso be VERY FLAT.. you can use a flat surface (granite, glass, marble etc.) with sandpaper on top to get it FLAT..
Also, don't cut (file) in the final tang shoulders until you finish hand sanding the ricasso, because you will end end rounding over the edges of the shoulders which will lead to a gap when ya get the guard fitted. Man, I say just read from the beginning lol

He covers all of this.. :thumbup: And of course the blade is the foundation for the guard, and so on and so on."
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Anyway, I can't stress enough that you read through that entire WIP if you haven't already (everyone else here will agree), it has hepled so many guys here in a bunch of differrent ways, myself included!
Also, click on this link check out his youtube channel:
Nick Wheeler Youtube channel
He has done many helpful videos that, just like his epic WIP, have helped many guys out, once again including myself

He covers proper hand sanding technique, shaping a bowie handle, grinding, how to dome a handle pin, forging, how to get perfect plunge line etc etc etc .. I'll just say watch as many of his videos as ya can.
Hope that helps!
~Paul
My YT Channel
Lsubslimed