We used the Revised Flat Galaxy Catalog ( RFGC ) to select 817 ultra-flat ( UF ) edge-on disk galaxies with blue and red apparent axial ratios of ( a / b ) _ { B } > 10.0 and ( a / b ) _ { R } > 8.5 . The sample covering the whole sky , except the Milky Way zone , contains 490 UF galaxies with measured radial velocities . Our inspection of the neighboring galaxies around them revealed only 30 companions with radial velocity difference of \mid \Delta V \mid < 500 km s ^ { -1 } inside the projected separation of R _ { p } < 250 kpc . Wherein , the wider area around the UF galaxy within R _ { p } < 750 kpc contains no other neighbors brighter than the UF galaxy itself in the same velocity span . The resulting sample galaxies mostly belong to the morphological types Sc , Scd , Sd . They have a moderate rotation velocity curve amplitude of about 120 km s ^ { -1 } and a moderate K-band luminosity of about 10 ^ { 10 } L _ { \odot } . The median difference of radial velocities of their companions is 87 km s ^ { -1 } , yielding the median orbital mass estimate of about 5 \times 10 ^ { 11 } M _ { \odot } . Excluding six probable non-isolated pairs , we obtained a typical halo-mass-to-stellar-mass of UF galaxies of about 30 , what is almost the same one as in the principal spiral galaxies , like M 31 and M 81 in the nearest groups . We also note that ultra-flat galaxies look two times less “ dusty ” than other spirals of the same luminosity .