#1
how do i know that the tuning machine that im buying will fit my guitar?
#2
the best way to do that is either to take the guitar to the store where you're gonna buy the tuning machines so they can measure it up for you.. or you can call your guitar's manufacturer and ask them about your tuning machines.. i think that's the best way, if you're unsure about the specs of your tuning machines..
Gear:

PRS SE Standard
Ibanez AEG8E-NT w/ Seymour Duncan Woody SC
Yupangco Classical Guitar
Korg AX5G
Marshall MG50DFX
Vox Pathfinder 15R
#3
you can look up the model of guitar and find out what size the stock tuners are, or do what the guy above me said, or if you have the right equipment for measuring the diameter of pegs and all that, you can do that.
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#4
well i took it to the store, but its been 4 wks and the thing still didnt come in yet, so i was just planning on buying online
#5
alright man.. good luck on that.. maybe you should follow it up from the store by phone from time to time so you'll know the progress of your orders..
Gear:

PRS SE Standard
Ibanez AEG8E-NT w/ Seymour Duncan Woody SC
Yupangco Classical Guitar
Korg AX5G
Marshall MG50DFX
Vox Pathfinder 15R