Hi Brenda;
I measured 4 bobbins & the winder spindle for my #8. The bobbins were consistent with a hole diameter through the hub of .232". The part of the spindle the bobbin fits on for winding is tapered. with the outer end being about .220" & the inner end going up to about .250" over a length of about 5/8" (.625"). You simply push the bobbin on until it is tight, there is no groove inside the hole to engage or no pin to engage the side of the bobbin, it is simply friction driven from the fit on the spindle.
The freer it turns the better, you do not want any drag on the winder. My winder has an over center cam which operates against a flat spring. It turns down for winding & up when not in use. The winder tire engages the flat on the bandwheel on the side next to the iron's leg. Wheel is of course outside the leg. You just throw the belt off in order not to run the machine while winding, there is no other release.
Miller/TN
