Each arm is sold individually - purchase the number you need to replace.
LOW - 4 Arms
MID - 4 Arms
TALL -4 Arms
If you are changing heights, you will also need to consider if your extrusion bars will be long enough. Here is a chart to help you identify what you need.
Extrusion Bar Lengths Needed by Rack Type:
Tacoma Low - 57"
Tacoma Mid - 53"
Tacoma Tall - 53"
Tundra Low - 63.5"
Tundra Mid - 60"
Tundra Tall - 60"
Colorado Low - 53"
Colorado Mid - 51"
Colorado Tall - 51"