Wanted: A stem and some help regarding it!

I just bought some new handlebars and they don't fit my current stem. The problem is, I'm a complete bike n00b and I have no idea about stem sizes or measurements or anything like that. Basically, the new bars are the dimensions of 63/40. I've tried to measure my stem and it seems to be about 2.4cm/0.9 inches although it has some larger silver nuts underneath it that make the base of the stem where it meets the frame about 3.2cm/1.2 inches. If anyone can help me out with what I need to ask for, for the right stem that would be awesome and if anyone has the right stem to sell me, then let me know and I'll buy it off you! Sorry for the length!

what handle bars are they?

pics

The handlebars are some Cinelli drops I bought from here. I'll upload pictures in a minute.

Cinelli bars are all 26.4mm clamp size. Simple way to make it all work is to ensure you use a cinelli stem too... now the question is whether the stem is Ahead or quill. does it look like an L shape like this

http://i1033.photobucket.com/albums/a420/CSFL/IMG_0072.jpg

Or like this

http://static.lfgss.com/attachments/27576d1278780932-005.jpg

(Pictures shamelessly stolen from FS threads on the forum, cheers all!)

If it is the former (a Quill stem) it will almost definitely be 1" and you could source a Cinelli quill to fit without too much difficulty. If the latter, you might need to check that it is 1 1/8" size (the most common size) but it could be 1".

Is the frame old or new?

...it has some larger silver nuts underneath it that make the base of the stem where it meets the frame...

Sounds like a threaded headset to me, and therefore likely you've got a quill stem as described by andyfallsoff^^^.

I'm guessing this is a quill stem then? I've attached some pictures below. Excuse the fact that it's a beater, I'm just building it cheaply to get some builiding experience and have some fun on a beater fixed gear.

5 Attachments

Yup, quill stem, 1" steerer (the actual external diameter of the quill is 7/8"). Remove it by undoing the allen bolt on the stem (apologies if this is getting into egg-sucking territory...).

I the new bars are the dimensions of 63/40.

63/40 is cinelli campione del mondo. 63 is model number and 40 is the overall width of the bars. nothing to do with the clamp size.
you need a cinelli 1A stem or something like it with a 26.4 clamp size. your black stem clamp is too small.
now before you go buy a 1A stem figure out if the length ( how far it reaches forward) of the stem is comfortable for you.mearsure the reach of your stem like this so you know what to look for because they come in 5mm increments

you can find a used 1A stem for as cheap as £5 for a beat up one all scratched up or you could buy this nice new one
http://www.lfgss.com/thread47670.html#post1541856

when you say the bars don't fit, do you mean they are too small/ large for the current stem?
you need to measure the diameter of the stem clamp area (where the stem would hold the bars), which will determine the size of the bars you need if you intend to keep that stem, other than that you need to buy a stem that will fit the bars you've just bought as stated above.

ahh, too slow

What loafheads said, plus, as you are using drops don't get a stem with too short a reach.