We use W.M. Berg's Gear Drive Chain.
http://precisionparts.wmberg.com/timingBeltsChains/cableChain-timingBelts (select Gear Drive Chains)
Part Number 24GCF-25FT (Note that you can buy it in different length increments as well)
Circular Pitch = 0.1309
Belt Width = 9/32"
Spec sheet attached.