I thought you had to vent a liquid gauge? we sell racor vac/press gauges that have the brass pin in top also, there is a plastic tape with writing on it that says, remove pin to read gauge, I got tired of removing the pin so I just chucked it on the murphy gauge, just gota install it with the hole facing up, I think the non vented liquid filled gauges are not for use in under hood installs cause of high temps, the gauges I use are not for racing or auto but seem to work fine but are a little pricey