You can get even fancier things with the inner hole to inflence your burn profile. For example, it can look like a star - this will give you high initial thrust as the burn area is big. As the inner spokes burn off, the burn front will star to approximate a circle, reducing thrust. This can be important to get you rocket the initial acceleration it needs to lift off but to avoid excessive acceleration destroying the rocket later on (as it it burning the rocket get lighter but the solid motor thrust would nornally stay the same or even grom slightly, due to the circular burn front being a bigger and bigger circle).