id halogen bulb?

[nealc]

Hi I have a bulb from an outdoor floodlight that needs to be replaced.  If possible, with an LED and/or a buglight.  So I measured it and it's about 3.1" so I'm thinking this is a 78mm.. I see lots of 78mm, but I'm wondering how finely these are measured, for example is there a difference between 3" and 3.1" and 3.2" or are these all just 78mm?

Thanks!