Sheesh. Leave it to a machinist to be pacific about it all! ;)
And aren't you glad such specifics are adhered to when such a machinist is grinding metal off your carby!!
Can we settle on 'brass'? Well, the needle jet is brass and usually isn't changed...but the needle (oem) is not brass and commonly IS changed....
OK, let's not settle on 'brass'.
When you make adjustments to your carb, you will be dealing with:
1. The main jet. A hex (six) sided jet that screws into the needle jet. You access it by taking the fuel bowl off, or by removing the plug that is at the bottom of the fuel bowl. Take it off/on with a 6mm socket. DO NOT OVERTIGHTEN! It's a snap (har-dee-har) to put too much twist on the main jet on install. Easy to break!!
2. The pilot jet. You must take the fuel bowl off to access this jet. It is directly in front of the main jet. You cannot easily see it unless you are looking 'up' into the carb. Access it with a small (1/8") common screwdriver.
3. The needle. This is accessed from the top of the carb. When you unscrew the top cap you can pull out the slide which has the needle bolted inside. Detach the throttle cable (check CDave's site for some handy ideas on holding the cable), unscrew the cable holder nut. Use a 6mm for this, too. Do not use a pair of pliers! The thing is hollow (because the throttle cable fits 'inside') and you can crush it easily. Do that and you won't be riding until you get a new one. Unscrew the holder and the needle is exposed. Just tip the slide upside down and the needle will drop out. Remove the clip to re-place on your new needle, or in a different slot on your existing needle. Caution is a good thing when dealing with this clip. It goes 's-p-r-o-i-n-g!' quite easily. If you're a profane,swearing person, you'll find there is a reason these are often called 'jesus clips.' Cuz when they DO go 'sproing'..you may say..well, you get the point.
Lose it and you'll be sorry, too. It is a metric-sized clip. A one-each clip from the local hardware store will not fit correctly without some filing (to the clip!! not the needle!!)
Drop the needle back in the hole in the slide, screw in the holder..insert your hemostat held cable. Note that the tang on the white nylon spring seat must seat in the slot in the holder!!
4. The slide itself. This is modified by changing the height of the cut on the front. You can do this yourself with a file if you're handy. Getting it to a machinist (one of those nit-picky guys! ;) ) is probably a good choice. Ron from RB-Designs can either cut your existing slide or sell you a differently cut slide. Choice #2 gets you something you can change back and forth..and there isn't any downtime due to shipping.
5. The airscrew. Access that using your small common screwdriver. Set for best throttle response. The 'high idle' setting is only a starting point. BTW..(also from Ron) you can get a finger adjustable screw so you can adjust the air screw..well..with your fingers. This isn't likely a big deal unless you have an RB modified carb. His modifications make that circuit much more useable than in its oem state, so adjustment is more frequent and more effective.
Before you do anything regarding rejetting on your kdx, please do check out CDave's site (linked in the 'Every kdx rider should read...' thread stickied to the top of this forum) for recommendations. That will get you in the ball park.
Whew! Asleep, yet? ZZZZzzZZZzzzZZZzz