Harken provides conveniently sized packages of replacement ball bearings. Common uses include traveler and batten cars. Size recommendations include: 3/16" Torlon for Micro CB Traveler Cars and Size AA Battcars 1/4" Delrin for Low Load Small Boat Traveler Cars and Size A Battcars 1/4" Torlon for High Load Small Boat Traveler Cars and Size A Battcars 5/16" Delrin for Low Load Midrange Traveler Cars and Size B Battcars 5/16" Torlon for High Load Midrange Traveler Cars and Size B Battcars 3/8" Torlon for all Big Boat Traveler Cars and Size C Battcars