I've got a 89 CRX with a DOHC ZC and I'm trying to hook up a pressure gauge at the filter, but I can't find a fitting that is small enough to fit where the service bolt comes out. Any ideas?

They make a banjo bolt that has a schrader valve in it. Remove the original, install the new one, hook up your gauge and your good to go. When your done install the original.

Just buy a B&M guage, they come with the fittings.