Originally Posted by
quiltingshorttimer
I agree and think the reason for this is that the metal in plastic may warp the case. I also wonder if there isn't some friction built up with bobbins/cases being different materials that might interfere with the machine computer.
Metal bobbins supposedly wear grooves in a plastic bobbin case over time. Personally, I've never seen it but I can see how it could happen. I use a metal bobbin in my Juki when it has the right color thread on it as I only have three plastic 15 class bobbins that came with it. I generally don't use this machine enough to worry about it.
Cari