if you look at my photo, the one on the upper left hand corner (along with most others) are low profile. It look like the mouse of your computer. The one on the bottom left hand corner is round profile...of cuase same with the bottom middle big one. It looks like an oil drum. It so happens that the low profile has the gear ratio of 6.2:1 and round profile has a lower gear ratio of 5.1:1. Lower gear ratio helps with the power of the reel.