It's one of the larger T-numbers I can tell you that! Go get a complete set from Snap on (best), or Sears (better), or Home Depot (good), or Harbor Freight (get's the job done). You will need a set of Torx to add to your tool collection eventually
OLD TIMMER H-D bikes have been using Torx for alot of fasteners since the 90's.
Gotta have em!