Search YouTube for long enough and you’ll find people successfully throwing and sticking all manner of objects from custom-made Bowie knives to needle-nosed pliers and everything in between! However, if you are looking to learn how to throw accurately and consistently, there are certain kinds of design that are better suited to throwing.
As a general rule, most purpose-made throwing knives tend to be between 10-16″ in length (25-40 cm) with a weight to length ratio of 1 ounce per inch of length (28 g to 2.5 cm). Beginners often favour a heavier knife because they tend to be more forgiving if form and skill isn’t quite dialled in.
Typically throwing knives will be weighted so that they balance at the centre of their length, allowing for an even rate of spin.
The two most common materials are carbon steel or stainless steel; there are pros and cons to both metals. As a rule, carbon steel has more flex and so can take punishment and burrs are more easily ground out but it has a tendency to rust and needs maintenance. In contrast stainless steel blades are more brittle and harder to work but they are impervious to the elements.
Contrary to what Hollywood might have us believe, a decent throwing knife does not need to be razor sharp; in fact that would be a design flaw for all but the most specialised of knives, designed for combat applications. In most cases a dull edge and a point but not a particularly aggressive one will do just fine, as long as the weight, length and balance are suitable.