GWS prop numbers provide you with the specification of the prop:
e.g. a GWS5030 prop has a diameter of 5.0" and a pitch of 3.0" (hence '5030')
The pitch of a prop refers to it's 'bite'. For every rotation of the prop, the prop will move forward by the pitch dimension in a static medium. So the larger the pitch number, the more 'aggressive' the bite.