[EricH]

"Each set" is the determiner.

1 set of bumpers goes on the robot every match and covers all four (five, three, six, etc.) sides.

Therefore each set of bumpers that goes on the robot can weigh 20 lbs. Fasteners are included depending on what is permanently attached to the bumper and what is not (<R07-J>).

Short version: all bumpers on the robot at any one time should weigh less than 20 lbs with all attachment hardware.