Question about stem
 

this has little to do with singlespeeds or fixed gears other than this is on a singlespeed.

the handlebars i intend to use have a bar end diameter of 26 mm. would that mean that i should get a stem with a clamp diameter of 26 mm also. I know that the handle bar gets thicker at the point where the stem would clamp so i'm not sure how that works.

It should fit without a problem on a modern 2 piece stem with a 1 inch/25.4 mm clamp; you'll have to use a shim if you have a stem with an oversized stem.

But if you have an old style/ njs quill stem; it won't fit and remove easily without probably damaging the quill....

so, i should get a slightly smaller stem then?

You would use shims if the bars had a smaller clamp diameter than the stem. So I guess it would be safer to get a larger stem.

31.8mm is a common oversized stem... ;)

I just love my oversized truvativ hussefelt risers which are 31.8 :D

If you want to keep your options open then get a stem with a 31.8 mm clamp. That way you can use a wide variety of bars, ranging from 25.4 to 31.8... just get a shim for the smaller ones. I actually wish I'd thought of this when I got mine. The set of track drops I wanted only comes in 31.8 mm and won't fit my tiny 25.4 mm stem. :'(

Oh and remember to also buy check steer tube diameter. Would suck to get a new stem that fits your handlebar perfectly but is too tight or too wide for your steer tube. Usually it's either 1" or 1 1/8".

If you're sure the bar end is 26.0mm and the center clamp area is thicker, then you know for sure you'll need a clamp size larger than 26.0.
A common clamp size is 31.8 and less common Italian 26.4.

Are you sure it's 26mm at the ends, and not just in the center?

When companies give a bar diameter, they are usually talking about the center diameter. That's to help you get the right stem. A 26mm handlebar would take a 26mm stem. Very common quill stem size. New bars also can come in the OS size or 31.8mm The ISO standard is 25.4mm and you find that on a lot of upright style handlebars. http://sheldonbrown.com/gloss_ha-i.html#handlebar

Cinelli used to make their bars and stems 26.4mm before adopting the 26mm so if you get Cinelli bars used from somewhere, make sure you know the correct size. Shimming can be done but I don't recommend it. Having your bars come loose at high speed is no fun at all.

Tell us what bars you've got.