Ye olde barrel adjusters for brake hangers and shifter stops. And fits rear derailleurs, too. And many brake calipers and some brake levers, too. And brake cable stops. Holy cow—best bring half a dozen spares with you even on your two-mile commute.
Sold individually, limited to four per household, per day, but we won't keep track.
Steel, black, slotted or Aluminum, silver, unslotted. Mix 'em, match 'em, go to town.
