Class M bobbins for longarm
I've been looking at class M bobbins and there seems to be 3 different kinds. One just has a hole in the center, the other has a hole and slot (similar looking to a class L) and the other has holes all around (similar in looks to a metal class 15). Are these all interchangeable in longarm machines that take the class M? If so, which would be the most popular or desired?
Also do longarmers usually buy prewound bobbins or prefer to wind their own?
This is for a swap on another board and all I know is the person wants class M bobbins for her longarm. Thanks!