In Sweden we make the best butter knives. We like butter. To treat the butter with proper respect you need a proper butter knife.
Making a butter knife out of metal, or even worse plastic, simply does not make the softness and golden creaminess of the butter justice.
Butter knives must be made out of slightly dark, big grained, flexible wood with a slight scent of fresh spring forest.
Thickness is important, so as to get the right flex when scooping up the butter with a precise sweeping motion (just the right amount, wiping excess butter from the knife on to the sides of the box is a capital offense when it comes to proper butter worshipping in Sweden) and the right resistance when applying the butter to the bread.
Another crucial factor, often done poorly in the cheap knockoffs we see flooding the country from places like Russia and Finland where they use any kind of crap wood for the butter knives, is of course the surface finish. Properly done, you should not be able to feel the difference between a swan feather and a Swedish butter knife stroking the inside of your thigh.
Swedish butter knives come in various shapes and sizes. Size is not important, neither is shape. The only important thing is that the handle is more narrow than the blade. It should be comfortable to hold and use, so nothing distracts you from enjoying the butter.
Some families in Sweden actually have individual butter knives, one for each family member. I have also dined with families where different knives are used for different kinds of bread, or different occassions (like Christmas, Easter, Midsummer and so on) depending on what time of year it is (can affect the quality of the butter, and type of bread used) if you are outside or indoors (affects the hardness of the butter) and if there is extra salt in the butter or not.
Above all, you must never use the butter knife to spread anything but butter! In doing so, the knife has been soiled and must be discarded from the box of butter knives making sure it doesn't spread the contanimation to the knives still pure.
There. An insight into the Swedish mentality, and how seriously we treat our butter.