New metal bike frames should have all of their threaded holes chased out with a tap.  To do this, you need self confidence, a steady hand, the approriate tap, cutting oil, and tap handle, plus a brass brush for post tappin’ clean up duties.  

You have to tap these holes out because if you don’t, when you go to install whatever, a derailleur or a bottle cage or a rack, you could easily cross thread the bolt.  If you are lucky, it will just damage the first two or three threads, but if you are unlucky, you will snap the bolt off in the frame, and then have to buy an expensive bolt extractor kit and hope it friggin works.  

People think that holes are tapped at the factory, but I can assure you that they are not.  Even custom US built frames are not tapped at the factory, at least not the ones I’ve seen.  

So what taps do you need for a new frame?  If the derailleur hanger is painted, you need a derailleur thread tap, and an m5 tap.  m5 taps are for 95% of all bottle cage, fender mount and rack mount holes.  If you have a Rivendell, you also need an m6 tap for the oversized rack mounts on the seat stays.  

We also keep pedal taps around, but they’re only important for either retaping cranks with damaged threads or converting french pedal threads to english. Nice to have, but not crucial.  

The way to use a tap: secure the tap in the tap handle.  Make sure it’s clean.  Give it a drop or two of cutting oil.  We like to use food grade cutting oil.  Then slowly start the tap in the hold.  The taper at the end should make centering it and starting it easy.  Go in a few turns, but if you feel resistance, back off a half turn before proceeding.  You might have to back off 10 times to tap one hole.  Better to go slow and back off, cleaning the threads by doing so, than forcing the tap.  Taps are very hard but brittle.  You can snap them.  Keeping a sharp tap is crucial.  As they wear, the cutting edge blunts, and taping is harder, and therefor easier to mess up.  Insert the tap until just a few threads are showing, then back off.  If there is a fair amount of resistance when you back the tap out, clean it and retap.