At 8pt, the middle horizontal line of 5 and 6 is touching the top horizontal line and ideally would appear one pixel lower. This is the case for Hack Regular and Hack Italic, but not Hack Bold nor Hack Bold Italic.
The middle horizontal line of 4 is one pixel higher when bold versus when not, though that's not necessarily a problem.
At 8pt, the middle horizontal line of 5 and 6 is touching the top horizontal line and ideally would appear one pixel lower. This is the case for Hack Regular and Hack Italic, but not Hack Bold nor Hack Bold Italic.
The middle horizontal line of 4 is one pixel higher when bold versus when not, though that's not necessarily a problem.