A bearing housing for a ram air fan, the bearing housing comprising: an inner housing portion centered on a central axis, the inner housing portion having a first end and a second end positioned axially away from the first end; an outer housing portion centered on the central axis, the outer housing portion having a first end and a second end positioned axially away from the first end, wherein the outer housing portion comprises: a radially outer surface having a diameter Doh1; a radially inner surface opposite of the radially outer surface, the radially inner surface having a diameter Doh2; and a shoulder on the first end of the outer housing portion, the shoulder having a radially outer surface with a diameter Ds that is smaller than the diameter Doh1 and larger than the diameter Doh2; a mounting flange having a ring shape extending radially outwards from the outer housing portion and positioned between the shoulder on the first end of the outer housing portion and the second end of the outer housing portion; and a disk portion connecting the second end of the outer housing portion to the second end of the inner housing portion; further comprising a plurality of first cooling holes extending through the disk portion, and a plurality of second cooling holes extending through the disk portion, wherein the plurality of first cooling holes and the plurality of second cooling holes are configured to allow cooling air to flow through the bearing housing from the first end of the outer housing portion to the second end of the outer housing portion, characterised in that the plurality of first cooling holes each have a diameter Dh1 and that the plurality of second cooling holes each have a diameter Dh2; wherein the diameter Dh2 of the plurality of second cooling holes is smaller than the diameter Dh1 of the plurality of first cooling holes, and wherein a ratio of the diameter Dh1 to the diameter Dh2 is between 3.1667 and 3.3367; wherein the plurality of first cooling holes includes five cooling holes positioned within a first disk sector of the disk portion and the plurality of second cooling holes includes four cooling holes positioned within a second disk sector of the disk portion positioned adjacent to the first sector of the disk portion. an inner housing portion centered on a central axis, the inner housing portion having a first end and a second end positioned axially away from the first end; an outer housing portion centered on the central axis, the outer housing portion having a first end and a second end positioned axially away from the first end, wherein the outer housing portion comprises: a radially outer surface having a diameter Doh1; a radially inner surface opposite of the radially outer surface, the radially inner surface having a diameter Doh2; and a shoulder on the first end of the outer housing portion, the shoulder having a radially outer surface with a diameter Ds that is smaller than the diameter Doh1 and larger than the diameter Doh2; a mounting flange having a ring shape extending radially outwards from the outer housing portion and positioned between the shoulder on the first end of the outer housing portion and the second end of the outer housing portion; and a radially outer surface having a diameter Doh1; a radially inner surface opposite of the radially outer surface, the radially inner surface having a diameter Doh2; and a shoulder on the first end of the outer housing portion, the shoulder having a radially outer surface with a diameter Ds that is smaller than the diameter Doh1 and larger than the diameter Doh2; a mounting flange having a ring shape extending radially outwards from the outer housing portion and positioned between the shoulder on the first end of the outer housing portion and the second end of the outer housing portion; and a disk portion connecting the second end of the outer housing portion to the second end of the inner housing portion; further comprising a plurality of first cooling holes extending through the disk portion, and a plurality of second cooling holes extending through the disk portion, wherein the plurality of first cooling holes and the plurality of second cooling holes are configured to allow cooling air to flow through the bearing housing from the first end of the outer housing portion to the second end of the outer housing portion, wherein the diameter Dh2 of the plurality of second cooling holes is smaller than the diameter Dh1 of the plurality of first cooling holes, and wherein a ratio of the diameter Dh1 to the diameter Dh2 is between 3.1667 and 3.3367; wherein the plurality of first cooling holes includes five cooling holes positioned within a first disk sector of the disk portion and the plurality of second cooling holes includes four cooling holes positioned within a second disk sector of the disk portion positioned adjacent to the first sector of the disk portion.