Grease!  If there is one thing that one should remember when installing handlebars and saddles, that thing would have to be grease.  Grease!

The handlebars are supported by the steering stem and the saddle, the seat post.  Before installing either the stem or the post, ensure that each is coated with a thin cover of grease.  This will significantly retard oxidation and prevent the components from becoming seized in their respective cavities.  And, a word of warning!  When one of these components becomes seized in its cavity, it is quite likely that the part will have to be destroyed before it can be removed. 

Before installing the stem or post, ensure that you have taken the time to prepare the frame set cavities.  If you fail to ensure that the cavities are prepared (clean, round, burr free, etc) you might well end up with a post that will not stay in place, or a stem that is difficult to install.

Few choices are offered with respect to seat post style.  In fact, two options present themselves.  The truly Old School heavy steel "pipe and clamp" assembly or the more modern, and far more "user friendly" alloy offering.  The modern seat post, by vintage road bicycle standards, is by far the best way to go if performance is the issue.  Performance being defined as staying put and easy to install/adjust a saddle on.  The modern unit is stronger, lighter, nicer looking, easier to mount a saddle on and offers more precise adjustment opportunities.  It is, however, not easier to install and more care must be taken to ensure that it does not become badly gouged due to improper installation and/or maintenance.

Hopefully, you will have given serious consideration to fit requirements before choosing your stem and handlebars.  The reach of the stem is an important issue, as is the width and drop of the handle bars, assuming that drop bars are those of choice.  And, once again, choice opportunities are many since the bicycle is a custom design and the builder is not limited to what is period correct, or original issue.

Believe it or not, slipping the handlebars into the steering stem can prove to be a daunting and damaging task if one does not know how to go about it.  Begin by ensuring that there are no burrs inside the steering stem clamp.  Take a moment to look and feel the inside diameter of the clamp and smooth out any offending bumps.  It is also a good idea to slightly bevel any edges.  Finally, a bit of dish washing soap smeared on the inside of the clamp and even on the center section of the handlebar can be a good idea if the assemble proves to be tighter that expected.

It is best to install handlebars into the stem before mounting the stem on the bicycle, however, be very careful when sliding the handlebars into the steering stem.  Move the bars slowly as you try to find the right position to allow each curve to slide through the stem.  It is very easy to find the wrong spot and think that extra pressure will help with installation, but it WON'T!  Forcing the bars to slide into the stem will likely result in gouging the soft alloy of the handlebars.  I have run across hundreds of beautiful vintage handlebars that have been badly scratched up.  Now, the scratches are no big deal if the occur only where they will be covered by handlebar tape.  But a slightly or badly scratched up middle section of the handlebars, the part where pantographing will be if there is any, is another story.  A set of Cinelli handlebars in nice condition will set you back fifty, sixty or seventy dollars at the time of this writing.  The same set with damaged pantographing is practically worthless.

Installing the seat post or steering stem are relatively straight forward tasks.  Both will usually have to be inserted a minimum amount to ensure safety.  This minimum insertion amount is often defined on the stem or post itself.  Failure to insert either to at least the "minimum insertion" mark could lead to an accident and/or damage to the bicycle itself.  If there is no mark indicated, insert the stem at least half way into the steering tube.  The unmarked seat post should be inserted a minimum of two and a half inches.

Installing the seat post is a simple as sliding it into the seat tube cavity and then tightening up the seat post clamp bolt.  Of course, before you tighten up the bolt, you must first know at what height to set the seat post.  And that height is defined when you fit yourself to the bicycle.  For the time being, just install the seat post at least to the minimum insertion line, snug it up and leave it.  And don't forget to grease the post first!

Though there are only two basic style choices for seat posts (pipe + clamp and indexed), there are several opportunities for adjustment.  Fore and aft, coupled with tilt angle and complicated by saddle height confuse the issue of finding proper saddle position.  There is no easy way that I can suggest to determine how far forward your saddle should sit.  Nor can I suggest the perfect angle of tilt.  What I can say is that I begin with the saddle sitting in the middle of the adjustment range of the saddle rails.  Try to set the angle of tilt so that the saddle top sits level to the floor, assuming that the floor is level to begin with.  This is your saddle's "starting position" to begin adjusting for best fit.  Without doubt, you will have to move the saddle forward or backward a bit.  And you will experiment with tilt.  But that part of the exercise will come when you are riding and getting to know the bicycle.  The adjustments that you make when first riding the bicycle will seem small but the results or your efforts will eventually be felt in the seat of your pants and for years to come.

Though it might seem a bit strange, the saddle need not be installed in perfect alignment with the centerline of the bicycle.  Many riders, usually men, will point the nose of the saddle a degree or two to one side or the other.  The theory is that doing so makes extra riding room where extra riding room is needed.  Perhaps this is a guys only issue, but an issue none the less.  And, I might add, that the issue becomes more pronounced with age.  As an old man, I today tilt my saddle a bit more forward and offset it just a touch towards the drive side of the bicycle.

Steering stems are offered in different "reaches" to help accommodate fit requirements.  Stem reach determines how far forward the handlebars sit and can be adjusted only by changing stems.  I prefer a shorter reach which allows me a slightly more upright riding position.  The stem must also be installed at least to the minimum insertion depth.  I prefer to have my stems installed only to this depth since this allows the bars to be mounted as high as possible in relation to the saddle height.  Were I into going as fast as I can under racing conditions, I would probably want to install the stem a bit deeper into the steering tube of the forks.  This would allow for a lower and more aerodynamic riding position.  But I am an old guy and I install the stem high.  The point is, consider what you will be using the bicycle for when making this fit decision.

The steering stem must also be install in-line with the centerline of the wheel.  This is almost a no brainer but you would be surprised how many old road bicycles come my way with misaligned steering stems.  Align the steering stem to the wheel, not to the frame set's top tube!  With the bicycle resting on its wheels, turn the handlebars to either the left or right.  Grip the front wheel with your knees or lower legs.  Now, looking down on the steering stem, line front and back of the stem up with the centerline of the tire.  This is how you come close to best alignment.  You will, however, put the results to the test under riding conditions and find that a bit more fussing is required to get the stem perfectly aligned.

However, you won't be doing much riding unless you can stop.  The "Single Speed" now looks just like a bicycle.  The frame is assembled and the wheels are installed.  The saddle is in its "starting position" as are the handlebars.  And the drive is hooked up.  The bicycle is ready to go!  Now is the time to turn your attention to stop.  Brake installation becomes the next issue of priority when assembling a bicycle.