How much should I tighten the gauge on my heating oil tank?
Pipe thread differs from the type used on nuts and bolts. The threads on bolts are the same diameter from top to bottom. Pipe fittings have a smaller diameter at the bottom than at the top. Because of this the threads don't bottom out they just get tight. Based on the number of exposed threads I would say the fitting is tight enough. Oil tanks are vented to the atmosphere so there no issue of pressure buildup causing a leak.