Oh this is very interesting about different class 15 bobbins - I bought a 4-pack of metal one but the metal actually is very light and doesn’t feel to be made as well as the original metal bobbins that come with the machines. I can look for plastic bobbins if they are recommended for the 237? Re the extra thread guide, the thread has a tendency to flip out of the last 2 thread guides nearest the needle when sewing at top speeds and it seems as though one midway between the uptake lever and the needle area would probably control that better. Maybe bearisgray was referring to something else and will return to this thread .