Standard Steel Liquid Level Gages can be used on hydraulic reservoirs, gearboxes, bearing housings, crankcases, transformers and machinery oil reservoirs.  Their use can be extended to any industrial liquid level viewing application.  Fluid enters through the cross hole in the hollow lower bolt and the gage is vented into the tank through the cross hole in the top bolt.   The length between the center of the two bolts is referred to as the centerline.  Centerlines are available from 3" to 60".