The 50 is the weight of the thread, the 2 or 3 is the number of strands/ply...the 3 ply would have more strength than the 2 ply. I haven't used the YLI Mako thread, but have used other YLI threads and have always had good luck with them. I won a spool of the thread from Connecting Threads from my guild once, and loved it, so did order some more colors.