We previously reported that the estimated eddy current losses of very thin 3% Si-Fe strip-wound cores in the 500 Hz to 5 kHz frequency range agreed comparatively well with measured values. The eddy current losses were estimated by employing the number of domain walls in a modified Pry and Bean model. We observed the number of domain walls on outermost surfaces by SEM. In this study, in order to investigate the difference between the measured eddy current losses and the estimated losses below 500 Hz, we removed one by one the layers of a 3% Si-Fe strip-wound core, and examined the relation between the number of domain walls and the eddy current losses. In these experiments, the cross-sectional area of a strip-wound core had to be large enough to maintain a sinusoidal flux waveform during core loss measurements after several layers were removed. We also examined the use of continuous annealing to fabricate a long and very thin grain-oriented 3% Si-Fe strip.