Box Components Maximus Cromo Race HandlebarThe Box Maximus Handlebars are the first, modern, 31. 8, oversize bars designed specifically for BMX racing. When used with the BOX Delta or Hollow, or Promax Banger OS or Impact OS stems (currently the only BMX stems on the market compatible with the Maximus bars), you get the stiffest cockpit available. The added stiffness significantly improves bike handling while putting more upper body power into your pedal stroke. That means getting out of the