  Low-temperature specific heat (SH) is measured for the 12442-type
KCa$_2$Fe$_4$As$_4$F$_2$ single crystal under different magnetic fields. A
clear SH jump with the height of $\Delta C/T|_{T_c}$ = 130 mJ/mol K$^2$ is
observed at the superconducting transition temperature $T_c$. It is found that
the electronic SH coefficient $\Delta\gamma (H)$ quickly increases when the
field is in the low-field region below 3 T and then considerably slows down the
increase with a further increase in the field, which indicates a rather strong
anisotropy or multi-gap feature with a small minimum in the superconducting
gap(s). The temperature-dependent SH data indicates the presence of the $T^2$
term, which supplies further information and supports the picture with a
line-nodal gap structure. Moreover, the onset point of the SH transition
remains almost unchanged under the field as high as 9 T, which is similar to
that observed in cuprates, and placed this system in the middle between the BCS
limit and the Bose-Einstein condensation.
