The Whittler!
Generally, the term Whittler refers to a type of construction of a pocket knife. Made for work, it usually has some size, although there are several "Sunday" knives that share the configuration, in a more delicate format. I will leave it to you my friends, whether to call them whittlers, or not!
Most whittlers have two backsprings, with a large blade at one end of the knife, riding on both springs, and two smaller blades riding (one each) the other end of the springs. Much more difficult to fit together than a simple Jack, a whittler showcases the cutler's art, and was often a premium purchase.
Several handle shapes were used for whittlers; serpentine, sleeveboard, equal end, balloon and more.
Sometimes a long slim wedge separated the backsprings, like an extra liner. Others were constructed with parallel springs, and a few with tapered springs (much more rare).
Here are some modern Schatt&Morgan takes on the Balloon whittler;
Here are some more Balloons, with a slim sleeveboard at the bottom;
These two show you the difference between parallel and tapered backsprings, both without wedges;
These final pictures show you old and new Case serpentine whittlers, with wedged backsprings, and incidentally show a Redbone comparison (don't get distracted now

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So if you have any interesting variations, please post them! There are tons more that fall into this category.