I used a milling machine on mine.
A drill press with a brake cylinder hone mounted in it on low speed would probably work.
A lathe might work if you mounted the throttle body in the tail stock somehow and your tool bit in the chuck.

 

stock bore is 50mm.. but it tapper down to about 47 above the tb plates

gains,, for me right off the bat

 

same gains right off the bat, throttle response is much quicker

 

I installed one that I bought got few more hp but when I put a spacer with it big difference... Fuel mileage actually went up .75 mpg lol but throttle responce is much much better ...

 

you thought the spacer did something but it didnt at all unless you drive lightly now

 

Throttle body spacers don't do a damn thing on our trucks. Waste of time, money, and hood clearance.

 

actually i noticed a gain in power when i took mine off lol

 

Yup, TB spacers are just paperweights. On older TB injected vehicles, they would help a lot of the time. However, our trucks are port injected, so all a TB spacer does is delay the air from getting into the intake manifold by an extra millisecond. That has no positive effect whatsoever on the truck, sometimes even having an adverse effect on performance.

 

Hmm ok well I just so happen to have a dyno program "Dyno scanby auterra" and also "Nology Lap dyno" on my lap top ... I will "weather permitting" post sheets on here with and with out right or wrong with old tb and with new. We'll see what is actually right if its worth it or not.

 

I ended up taking that off and putting the stock one back on it felt much better