I'm pretty sure it's
this type. The early version had a thread guide, or "finger", moving the thread left and right to fill the bobbin evenly. The later version didn't have the moving finger, but a more minimal solution. There might be a few other differences; when you take of the belt guard notice the number of fitting screws and where are placed. My 1934 model 99 has the early type winder, I think they are the same as 66. I don't think the second type appeared until the 1940s, not sure there are a specific year of introduction, since features, version and production tend to overlap. It's at least so with model 15. Model 66 is luckily less fuzz than 15s, but there are a few surpises on this model too. The 66-8 are a much later version than yours, probably the first with stitch length lever and backtack in stead of the turn knob