Here is new pics of my Hira rubber shuriken's
to satisfy everyone's choice, it is possible to get them in several thicknesses(size is also possible to change),
my standard 4 mm thick are enough if throw them on your Uke, but if you do certain techniques of hitting or stabbing with Shuriken then you need something thicker, such as 6 to 6.5 mm thick, this thicker are also good for longer distance or more realistic feeling evasion of shuriken flying towards you, perhaps even metal but blunt.
My recommendation is always, get yourself a different (if not size) thickness for all types of training, only one species is not enough.
so here they are,