  Short-timescale microlensing events are likely to be produced by substellar
brown dwarfs (BDs), but it is difficult to securely identify BD lenses based on
only event timescales $t_{\rm E}$ because short-timescale events can also be
produced by stellar lenses with high relative lens-source proper motions. In
this paper, we report three strong candidate BD-lens events found from the
search for lensing events not only with short timescales ($t_{\rm E} \lesssim
6~{\rm days}$) but also with very small angular Einstein radii ($\theta_{\rm
E}\lesssim 0.05~{\rm mas}$) among the events that have been found in the
2016--2019 observing seasons. These events include MOA-2017-BLG-147,
MOA-2017-BLG-241, and MOA-2019-BLG-256, in which the first two events are
produced by single lenses and the last event is produced by a binary lens. From
the Bayesian analysis conducted with the combined $t_{\rm E}$ and $\theta_{\rm
E}$ constraint, it is estimated that the lens masses of the individual events
are $0.051^{+0.100}_{-0.027}~M_\odot$, $0.044^{+0.090}_{-0.023}~M_\odot$, and
$0.046^{+0.067}_{-0.023}~M_\odot/0.038^{+0.056}_{-0.019}~M_\odot$ and the
probability of the lens mass smaller than the lower limit of stars is $\sim
80\%$ for all events. We point out that routine lens mass measurements of short
time-scale lensing events require survey-mode space-based observations.
