Hi again, my 1600 has the side rotary bobbin. I'm not sure at all what all those letters stand for. I will go look at my book and see if I'm leaving some off. ha Okay, it only has the one letter, 1600 P. It is white with purple on it, does that help? ha I don't know what the other machines with more letters have that is different than mine. But oh my goodness, I bought it in Dec. of 2004, so guess I've had it nearly 6 yrs now! It does nothing but straight stitch, which is fine with me as I have the other machine to do zig zag, etc. Hope this helps.