Hershey, 90's have different size air tubes for premix, oil injected and sport models. These are the dimensions for 90 Sport oil injected and 90 Trail premix. I think there is one more? Hope this helps, Steve
90 Sport oil injected (all oil injected 90 models):
inside diameter 42.4mm/ outside diameter 45.2mm/ length 90.5mm
90 Trail premix (standard, mountain premix):
inside diameter 35.6mm/ outside diameter 38.0mm/ length 105.3mm