JST ans MOLEX are brand names. Wire to board and pitch (spacing between pins) you need to know.
There is 2.54 and 2mm for example and 1 and 1.27 and others. The 2.54 being 0.1"
You can measure with a camera and a reference. You can get the dimensions of a coin on line.
But a ruler or drill bit work.
You orient the scale, take a pic and proportional;y figure out another dimension.
I suspect the 5.5mm pitch is the outside dimension and it's actually 2.54mm pitch and center to center of the outer pins is closer to 5mm. Unless someone knows of a 2.75mm pitch connector.
I'm guessing one of the pins is slightly bent outwards, which is quite common with pin headers if the cable part does not pull away exactly square when it is disconnected.
I'm guessing one of the pins is slightly bent outwards, which is quite common with pin headers if the cable part does not pull away exactly square when it is disconnected.
I'm guessing a newbie measured outside of left pin to outside of right pin.instead of center-to-center (or right edge to right edge). That would give 0.1" + 0.1" + 0.025" =0.225" or 5.33mm (measured with a cheap plastic ruler, it looks close enough to 2.5mm).