The factory tach hole is 3 1/2 inches, which doesn't fit any standard Auto Meter gauge. So we decided to mount a 2-inch oil pressure gauge there along with a 5/16-inch light from Painless Performance for the high-beam indicator. The only problem we had was that the plastic panel didn't fit flush against the gauge opening. We faced the same problem for the new turn-signal indicators and the dash openings. We fixed this by cutting another smaller panel to house this gauge and the pair of 5/16-inch turn-signal indicators.