Cinelli Handlebar Problems

I have Cinelli handlebars on 3 separate bikes. None of them have a uniform diameter.

Two of them are Campione del Mondo 66 models, both in Cinelli XA stems. They both occasionally slip in the stem, particularly on descents having resulted in more than a few sh!t my pants moments. My first thought was perhaps they were 26.0 bars in 26.4 stems . But measuring the bars in the calipers I can't get consistent readings, they seem to average around 26.2 . Is it safe to assume these are 26.4 but perhaps worn? I'm assuming the stem is 26.4 as surely 26.4 bars wouldn't fit in a 26.0 stem?

Both XA stem clamps are tightened to the point where the two outer edges of the slot for the rubber grommet are pretty much touching, i.e. not parallel. I'm worried this is gong to lead to the stem cracking around the face plate.

The third set I have are a pair of NOS Top 66 Ergos. They were sold to me by Planet X as 25.4 ( I wondered at the time if Cinelli had produced this size later on but can find no evidence of this) . Horizontally they measure as 26.02, vertically 26.4 and numerous variations in-between. I have these fitted in a 3TTT Record 84 stem which is supposed to be 25.8. They don't slip but I still don't understand what size they are.

What is going on here? Aside from buying the new release Cinelli bars and stems I don't know what to do? Am I asking for an impending pavement sandwich?

Both XA stem clamps are tightened to the point where the two outer edges of the slot for the rubber grommet are pretty much touching, i.e. not parallel.

That sounds bad, ie the bars are too small for the stems: 0.2mm could come from anywhere. Having said that I thought XA were a later model, ie 26.0mm.

a pair of NOS Top 66 Ergos

I thought 3t only made 26.0mm, they certainly didn't make 26.4mm so the bars must be 26.0mm. I don't understand what you mean by horizontal and vertical measurements.

Cheers, I meant measuring holding the calipers horizontally i.e. measuring the central sleeve from front to back , or vertically, from top to bottom of the central sleeve ..

Ill try to post a photo of the XA stem tomorrow.

Here's a photo, it's a bit hard to see but the outside edges of the gap for the rubber insert (where the bolt goes) are almost touching forming a v shape . Admittedly the bar slip was worse before I got the rubber insert (the stem came without one) Should it be this tight with the rubber squashing out the sides or should the two surfaces either side of the rubber remain parallel when tightened ?

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It seems the XA came out earlier than I thought (mid-eighties), so would have been available in 26.4mm. It had quite a long production run though, so quite likely could be had in 26.0mm.

Either way, no that does not look right to me: I'd say the stem is too big for the bars.

I don't wish to alarm you unduly with third-hand internet gossip, but supposedly they suffer in the same way as the "Modolo Death Stem"...

If you do a bit of trawling you'll get a handle on the old and new style Cinelli logos, which will broadly separate the 26.0mm from the 26.4mm.

Thanks, I'm pretty sure I purchased both bars as 26.4 so I'm not sure I can trust 2nd hand due to the inaccurate readings. Best bet might be to buy one of the new release 26.0 1A stems. Problem is if the bars don't fit its unlikely Ill be able to return the stem ! I did try a coke can shim a while back but that made them slip more for some reason .