I found two youtube videos, it looks like it takes class 15 bobbin and bobbin case. Several of the older models were given the new look in the early 1950s; the 99 became 185, the old 201 were given an aluminium body with the updated design 201K23. The old 15 were given a new body, several versions of it; black, beige, green. I know some complain the 185 has a more noisy motor than the old 99s. I guess it could be the motor design, but of course cleaning, regreasing and new belt makes all the difference too. The 191 could be a derivative of the old 15?