We use W.M. Berg's Gear Drive Chain.
http://precisionparts.wmberg.com/timingBeltsChains/cableChain-timingBelts  (select Gear Drive Chains and scroll down to correct part number)
Part Number 24GCF-50FT (Note that you can buy it in different length increments as well)
Circular Pitch = 0.1309
Belt Width = 9/32"
Spec sheet attached.