Hello Leatherworkers! From Pilgram Sewing Supply I bought the parts to convert my 31-15 to a roller foot (S-194 Foot bar, needle plate and feed dog).  The roller foot on the new foot bar is small (and doesn't swing open to the side), so I went to my local sewing machine repair shop and picked up a larger roller foot, which does swing open.  When I brought the larger roller foot home, I noticed that it doesn't seem to be compatible with the foot bar...is there something that I am not seeing?