I have an OLP MM1FR (Ernie Ball Music Man "EVH/Axis" copy) guitar that came with a very cheap "licensed" Floyd tremolo. I want to upgrade to a German-made Floyd Rose, and I need to know which locking nut to order. I dont know how to measure the neck, and I couldn't find any OLP factory measurement info on the web.

Any assistance is greatly appreciated.

You shouldn't need to replace the locking nut unless you're having trouble finding a colour match on the floyd. All the locking nuts do is lock the strings in place. If they work, they work.
There is no need to replace the locking nut if it works, unless you want to change the colour.
Measurements are taken lengthwise across the nut. It usually is about 42/43 mm. They go very cheap on Ebay, even for OFR.
What tremolo did you end up putting in your mm1fr I was thinking of do the same to mine.....considering GE1996TC gotoh if it will fit, im still researching to see if it will
Just look up the specs for a Licensed Floyd Rose all of the chinese made ones are the same; however I thought the specs were the same as the real deal Flyod rose and it was just made out of shitty metals in comparison.
2011 Gibson Honeyburst LP Trad. w/ SD Whole Lotta Humbuckers
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Be sure to check the sustain block length on your OLP. If you only have space for a 32 mm sustain block, a 42 mm will stick out the back of your guitar a small amount.