What is a bobble? 
Bobbles are drums of stranded yarn. The yarn is not twisted/plied. Instead, the 4 strands of yarn run alongside each other. Only one strand changes colour at any one time, resulting in a gradient colour change, also known as a fade. 
I most often wind the bobbles in 1000m length, sufficient for a large shawl. This is equivalent to 270g or 6 balls of yarn. A 500m/133g bobble is the smaller version and is ideally combined with another bobble for endless colour play. Or just a smaller shawl. 
The weight is similar to 4ply/fingering and the recommended needle size is 3-4mm (US 2-6). For a garter stitch project, a 4mm (US 6) gives a drapey fabric. For mosaic or other stripey patterns, as well as lace patterns, a 3.25mm needle gives a clearer definition.