public static readonly fields are a little unusual; public static properties (with only a get) would be more common (perhaps backed by a private static readonly field).

const values are burned directly into the call-site; this is double edged:

  • it is useless if the value is fetched at runtime, perhaps from config
  • if you change the value of a const, you need to rebuild all the clients
  • but it can be faster, as it avoids a method call...
  • ...which might sometimes have been inlined by the JIT anyway

If the value will never change, then const is fine - Zero etc make reasonable consts ;p Other than that, static properties are more common.