Hello, Meznik : it sure is a small bobbin,just got this machine and have been cleaning it up, when I was young this machine was at a friends home,and always told him I wanted it ,now 55 years later it come's to me.take's a little getting use to but got it stitching like a big dog.found an other one on line for parts.earlier model but so far the parts match. got the bobbin from it. will try that Singer 29k just to see if it is dementioned properly . the shaft on the bobbin holder is 3.11mm,and the holds on the bobbin is 3.20mm. that is how much of a gap there is. not much ,but lets the thred move along just fine.If you come across more than you need please let me know.intrested in purching a few,or know where to get some.remember in the bottom of the bobbin holder there is a screen of some sort that holds a drop or 2 of oil.makes the bobbin work 100 times better.GET STICHING MON AMY.Regard David