bainin wrote:To be honest-I don't really have a firm idea how to tell exactly what I have but I "think" its a 520.
Since you say you bought it used, it may have had upgrades. The sticker on the headstock and/or the model number should say what model it started out as.
The table size and configuration is best way to differentiate (at least for me). Each type also has a specific fence for use with it, and there are variations in rail details, but basically:
A 500 table is smaller and has no rails for connecting floating tables.
A 505 and 510 table have round rails in front and back for connecting pipes.
A 520 has extruded aluminum rails front and back for connecting pipes.