Please note the “M” stands for magnetic.
They are the same bobbin case as 52237, except the “M” has a magnetic core that helps keep the bobbin from vibrating, which can cause overspin and backlash, leading to thread breakage.
Guaranteed to fit Singer Sewing Machine Models:100, 1300, 1400W, 183, 188K, 188K1, 191, 195, 195K, 241, 241-11, 241-12, 241-13, 245, 251, 281, 281-1, 281-3, 281-21, 291U, 331K, 366K, 400W, 451K, 491, 600A51, 600W, 660A, 660W, 701-710, 749-4, 749-5, 761-765, 95, 95-10, 95-11, 95-12, 96-18, 96-41, 95-80, 96, 96-10, 96-12, 96-13, 96-15, 96-16, 96-3, 96CL