Many (called ninja stars). The term shuriken really means something close to "knife concealed in the hand". This implies spike essentially any little, hand held knife or spiked wheel are really shuriken.
Trembled come in various fashions, shapes as well as distinct sizes. Not ryuha or every school has their particular layout as some consider, some will share layouts.
Many shaken designs known as senban were derived from carpenter's tools including prying tools and nail pullers (the claw hammer was never devised by the Japanese). They were simple to make and disguise since they were trivial carpentry tools.
Another common misconception is the fact that all had sharp edges. Many designs didn't. The explanation for that is many ryuha educate using shaken within hand to hand combat or their taijutsu. The shaken are used as hand blades, force multipliers, brass knuckles, fist loads also to hit to pressure points. A shaken that's sharpened on all sides and borders would cut against the wielder just as much if used this way as it could cut the target. Picture you reached into your gi to pull a shaken out and cut yourself and if it was poisoned? A possibly disastrous error.
I've personally seen straightforward unsharpened Togakure fashion senban will go through either side of a 2' x 2' cardboard box, out stick and another side .
That is misconception pictures and media including Revenge of the Ninja (1983). A shaken's true purpose was cause or to divert inconveniencing harm to hands or the face thereby reducing the rivals effectiveness. It will not require much to cause hand harm or a debilitating face like these bleed more than other areas of the body. Evan a little cut the facial skin can cause blood in a hand wound as well as the eyes can cause blood to alternative weapon or the sword grip which makes it glossy.