how to identify a nozzle of 0.48 or 0.4?

i am having problems of extrusion and i suspect of the nozzle, it dosent had any mark that says 0.48 or 0.4, when i heat the hotend and manualy push pla in the hotend to get a string i get string of .50 .48 mm of widht, but when i try this tutorial [solidoodletips.wordpress.com] i get 0.43 to 0.5 wall thickness, so i dont know if i need to adjust the extrusion multiplier or i putting a bad nozzle diameter in the slic3r

Dont measure the extruded filament. Its probably a .4mm its the most typical nozzle.

High temperature can also make the extrusion fatter. Not just the extrusion, but it melts the layer below and can cause slumping.
What happens if you drop it by 5c 10c and 15c?

Can you upload a photo?

best bet get a set of nozzle drills and see what fits or make it size you want