[sly mantis]

Hi
Recently picked up some nozzles for a g36 and mp5. i decided to measure them just to confirm and found that they were shorter than i expected them to be from looking online at specs.
The g36 nozzle measured 23.5mm vs 24.3 spec i found online and the mp5 was 18.0mm vs 20.4mm spec. Pics attached, these are shs nozzles.

Im wondering if im either measuring these the wrong way, i got the wrong part, or are there different lengths for different versions of these guns?

Thanks